How to enable featured image for category and tags?

Things we will proceed with:
1. edit Functions.php
2. Create featured-image-for-categories.php file in theme or child theme
3. Two placeholder Images inside theme folder: placeholder.png and placeholder-thumb.png

Step1. Add this code to functions.php file

include('featured-image-for-categories.php');
new WP_Simple_Featured_Image;

Step2 : Create a new file with name “featured-image-for-categories.php” and add the below code to this file.

<?php
if (!defined('ABSPATH')) {
    exit; // Exit if accessed directly
}


class WP_Simple_Featured_Image{
    public $wpsfi_taxonomy = array();
    public function __construct(){
        $wpsfi_taxonomy         = get_option( 'wpsfi_taxonomy' );
        $wpsfi_post_type        = get_option( 'wpsfi_post_type' );
        $this->wpsfi_taxonomy   = $wpsfi_taxonomy;
        if( !empty( $wpsfi_taxonomy ) ){
            foreach( $wpsfi_taxonomy as $taxonomy ){
                add_action( $taxonomy.'_add_form_fields', array( $this, 'featured_taxonomy_field' ) ); 
                add_action( $taxonomy.'_edit_form_fields', array( $this, 'edit_featured_taxonomy_field' ) ); 

                // manage_edit-product_cat_columns
                add_filter('manage_edit-'.$taxonomy.'_columns', array( $this, 'taxonomy_columns_header' ) );
                add_filter('manage_'.$taxonomy.'_custom_column', array( $this, 'taxonomy_columns_content_taxonomy' ), 10, 3 );
            }
        }     
        if( !empty( $wpsfi_post_type ) ){
            foreach ( $wpsfi_post_type as $post_type ) {
                add_filter('manage_edit-'.$post_type.'_columns', array( $this, 'post_columns_header' ) );
                add_filter('manage_'.$post_type.'_posts_custom_column', array( $this, 'post_columns_content' ), 10, 2 );
            } 
        }

        add_filter('manage_edit-post_columns', array( $this, 'post_columns_header' ) );
        add_filter('manage_posts_custom_column', array( $this, 'post_columns_content' ), 10, 2 );

        add_action( 'created_term', array( $this, 'save_wpsfi_taxonomy_fields' ), 10, 3 );
        add_action( 'edit_term', array( $this, 'save_wpsfi_taxonomy_fields' ), 10, 3 );

        add_action('admin_menu', array( $this, 'settings_menu' ) );
        add_action( 'admin_init', array( $this, 'register_setting_options' ) );

        add_action( 'admin_enqueue_scripts', array( $this, 'admin_scripts' ) );
    }

    public function admin_scripts(){
        wp_enqueue_media();
    }

    public function register_setting_options(){
        register_setting( 'wpsfi_settings_group', 'wpsfi_taxonomy' );
        register_setting( 'wpsfi_settings_group', 'wpsfi_post_type' );
    }


    public function settings_menu(){
        add_submenu_page(
            'options-general.php',
            __( 'Featured Image Settings', 'wp-simple-featured-image' ),
            __( 'Featured Image Settings', 'wp-simple-featured-image' ),
            'manage_options',
            'wpsfi-settings',
            array( $this, 'settings_menu_callback' )
        );
    }

    function save_wpsfi_taxonomy_fields( $term_id, $tt_id = '', $taxonomy = '' ){
        $wpsfi_taxonomy = $this->wpsfi_taxonomy;
        if( empty( $wpsfi_taxonomy ) ){
            $wpsfi_taxonomy = array();
        }
        if ( isset( $_POST['wpsfi_tax_image_id'] ) && in_array( $taxonomy, $wpsfi_taxonomy )  ) {
            update_term_meta( $term_id, 'wpsfi_tax_image_id', $_POST['wpsfi_tax_image_id'] );
        }
    }
    
    public function settings_menu_callback(){
        ?>
        <h1><?php _e('Featured Image for Categories and Custom Posts', 'wp-simple-featured-image' ); ?></h1>
        <p class="description"><?php _e('Select taxonomies you want to enable Featured Image.', 'wp-simple-featured-image' ); ?></p>
        <form method="post" action="options.php">
            <?php
			
			echo get_option( 'wpsfi_post_type' ).'test';
            settings_fields( 'wpsfi_settings_group' );
            do_settings_sections( 'wpsfi_settings_group' );
            $wpsfi_taxonomy     = get_option( 'wpsfi_taxonomy' ) ? get_option( 'wpsfi_taxonomy' ) : array() ;
            $wpsfi_post_type    = get_option( 'wpsfi_post_type' ) ? get_option( 'wpsfi_post_type' ) : array() ;
            $registered_taxonomies  = wpsfi_get_registered_taxonomy();
            $post_type_list         = wpsfi_post_type_list();
            ?>
            <table class="form-table">
                <tr>
                    <th><?php _e('Select Taxonomy to Display Featured imgae', 'wp-simple-featured-image' ); ?></th>
                    <td>
					
                        <?php if( !empty( $registered_taxonomies ) ): foreach( $registered_taxonomies as $key => $value): ?>
                        <input type="checkbox" name="wpsfi_taxonomy[]" value="<?php echo $key; ?>" <?php echo ( in_array( $key, $wpsfi_taxonomy ) ) ? 'checked' : '' ; ?>> <?php echo $value; ?><br/>
                        <?php endforeach; endif; ?>
                    </td>
                </tr>
                <tr>
                    <th><?php _e('Select Post Type to Display Featured imgae', 'wp-simple-featured-image' ); ?></th>
                    <td>
                        <?php if( !empty( $post_type_list ) ): foreach( $post_type_list as $postType): ?>
                        <input type="checkbox" name="wpsfi_post_type[]" value="<?php echo $postType; ?>" <?php echo ( in_array( $postType, $wpsfi_post_type ) ) ? 'checked' : '' ; ?>> <?php echo $postType; ?><br/>
                        <?php 
						
						endforeach; 
						
						else:
						
						echo 'No custom posts found!';
						
						endif; ?>
                    </td>
                </tr>
            </table>
            <?php submit_button( __( 'Save Settings', 'wp-simple-featured-image' ) ); ?>
        </form>
        <?php
    }
    function taxonomy_columns_header( $defaults ){
        $defaults['wpsfi_featured_image']  = __('Featured Image', 'wp-simple-featured-image' );
        return $defaults;
    }
    function taxonomy_columns_content_taxonomy( $columns, $column, $id ){
        if ( 'wpsfi_featured_image' === $column ) {
            $imageID = get_term_meta( $id, 'wpsfi_tax_image_id', true );
            $image_url = wpsfi_get_featured_image_url( $id );
            $columns .= '<img data-id="'.$imageID.'" src="' . esc_url( $image_url ) . '" alt="' . esc_attr__( 'Thumbnail', 'wp-simple-featured-image' ) . '" class="wpsfi-image" height="48" width="48" />';
        }
        return $columns;
    }
    function post_columns_header( $defaults ){
        $defaults['wpsfi_featured_image']  = __('Featured Image', 'wp-simple-featured-image' );
        return $defaults;
    }
    function post_columns_content( $column, $post_id ){
        if ( 'wpsfi_featured_image' === $column ) {
            if( has_post_thumbnail( $post_id ) ){
                echo get_the_post_thumbnail( $post_id, array( 48, 48) );
            }else{
                echo '<img src="'.wpsfi_placeholder_image(false).'" alt="Thumbnail" class="wpsfi-image" height="48" width="48">';
            }
        }
    }
    public function featured_taxonomy_field(){
        ?>
        <div class="form-field wpsfi_taxonomy_featured_image">
            <label><?php _e( 'Featured Image', 'wp-simple-featured-image' ); ?></label>
            <div id="wpsfi_tax_image" style="float: left; margin-right: 10px;"><img src="<?php echo esc_url( wpsfi_placeholder_image() ); ?>" width="60px" height="60px" /></div>
            <div style="line-height: 60px;">
                <input type="hidden" id="wpsfi_tax_image_id" name="wpsfi_tax_image_id" />
                <button type="button" class="upload_image_button button"><?php _e( 'Upload/Add image', 'wp-simple-featured-image' ); ?></button>
                <button type="button" class="remove_image_button button"><?php _e( 'Remove image', 'wp-simple-featured-image' ); ?></button>
            </div>
            <script type="text/javascript">
                jQuery(document).ready( function($){
                    if ( ! $( '#product_cat_thumbnail_id' ).val() ) {
                        $( '.remove_image_button' ).hide();
                    }
                    var file_frame;
                    $( 'body' ).on( 'click', '.upload_image_button', function( event ) {
                        event.preventDefault();
                        if ( file_frame ) {
                            file_frame.open();
                            return;
                        }
                        file_frame = wp.media.frames.downloadable_file = wp.media({
                            title: '<?php _e( 'Choose a Fetured Image', 'wp-simple-featured-image' ); ?>',
                            button: {
                                text: '<?php _e( 'Use as Fetured Image', 'wp-simple-featured-image' ); ?>'
                            },
                            multiple: false
                        });
                        file_frame.on( 'select', function() {
                            var attachment           = file_frame.state().get( 'selection' ).first().toJSON();
                            var attachment_thumbnail = attachment.sizes.thumbnail || attachment.sizes.full;
                            $( '#wpsfi_tax_image_id' ).val( attachment.id );
                            $( '#wpsfi_tax_image' ).find( 'img' ).attr( 'src', attachment_thumbnail.url );
                            $( '.remove_image_button' ).show();
                            $( '.upload_image_button' ).hide();
                        });
                        file_frame.open();
                    });

                    $( 'body' ).on( 'click', '.remove_image_button', function() {
                        $( '#wpsfi_tax_image' ).find( 'img' ).attr( 'src', '<?php echo esc_js( wpsfi_placeholder_image() ); ?>' );
                        $( '#wpsfi_tax_image_id' ).val( '' );
                        $( '.remove_image_button' ).hide();
                        $( '.upload_image_button' ).show();
                        return false;
                    });

                    $( 'body' ).ajaxComplete( function( event, request, options ) {
                        if ( request && 4 === request.readyState && 200 === request.status
                            && options.data && 0 <= options.data.indexOf( 'action=add-tag' ) ) {

                            var res = wpAjax.parseAjaxResponse( request.responseXML, 'ajax-response' );
                            if ( ! res || res.errors ) {
                                return;
                            }
                            $( '#wpsfi_tax_image' ).find( 'img' ).attr( 'src', '<?php echo esc_js( wpsfi_placeholder_image() ); ?>' );
                            $( '#wpsfi_tax_image_id' ).val( '' );
                            return;
                        }
                    } );
                });
            </script>
            <div style="clear:both;"></div>
        </div>
        <?php
    }
    public function edit_featured_taxonomy_field( $term ){
        $thumbnail_id = get_term_meta( $term->term_id, 'wpsfi_tax_image_id', true );

        if ( $thumbnail_id ) {
            $image = wp_get_attachment_thumb_url( $thumbnail_id );
        } else {
            $image = wpsfi_placeholder_image();
        }
        ?>
        <tr class="form-field">
            <th scope="row" valign="top"><label><?php _e( 'Featured Image', 'wp-simple-featured-image' ); ?></label></th>
            <td>
                <div id="wpsfi_tax_image" style="float: left; margin-right: 10px;"><img src="<?php echo esc_url( $image ); ?>" width="60px" height="60px" /></div>
                <div style="line-height: 60px;">
                    <input type="hidden" id="wpsfi_tax_image_id" name="wpsfi_tax_image_id" value="<?php echo $thumbnail_id; ?>" />
                    <button type="button" class="upload_image_button button"><?php _e( 'Upload/Add image', 'wp-simple-featured-image' ); ?></button>
                    <button type="button" class="remove_image_button button"><?php _e( 'Remove image', 'wp-simple-featured-image' ); ?></button>
                </div>
                <script type="text/javascript">
                    jQuery(document).ready( function($){
                        var tax_thumbnail = $( '#wpsfi_tax_image' ).val();
                        if ( '0' === tax_thumbnail || '' === tax_thumbnail ) {
                            $( '.remove_image_button' ).hide();
                        }
                        var file_frame;
                        $( 'body' ).on( 'click', '.upload_image_button', function( event ) {
                            event.preventDefault();
                            if ( file_frame ) {
                                file_frame.open();
                                return;
                            }
                            file_frame = wp.media.frames.downloadable_file = wp.media({
                                title: '<?php _e( 'Choose a Fetured Image', 'wp-simple-featured-image' ); ?>',
                                button: {
                                    text: '<?php _e( 'Use as Fetured Image', 'wp-simple-featured-image' ); ?>'
                                },
                                multiple: false
                            });
                            file_frame.on( 'select', function() {
                                var attachment           = file_frame.state().get( 'selection' ).first().toJSON();
                                var attachment_thumbnail = attachment.sizes.thumbnail || attachment.sizes.full;
                                $( '#wpsfi_tax_image_id' ).val( attachment.id );
                                $( '#wpsfi_tax_image' ).find( 'img' ).attr( 'src', attachment_thumbnail.url );
                                $( '.remove_image_button' ).show();
                                $( '.upload_image_button' ).hide();
                            });
                            file_frame.open();
                        });

                        $( 'body' ).on( 'click', '.remove_image_button', function() {
                            $( '#wpsfi_tax_image' ).find( 'img' ).attr( 'src', '<?php echo esc_js( wpsfi_placeholder_image() ); ?>' );
                            $( '#wpsfi_tax_image_id' ).val( '' );
                            $( '.remove_image_button' ).hide();
                            $( '.upload_image_button' ).show();
                            return false;
                        });
                    });
                </script>
                <div style="clear:both;"></div>
            </td>
        </tr>
        <?php
    }
}



/* ++++++++++++++++++++++++ Display +++++++++++++++++++++++++*/

function wpsfi_placeholder_image( $default = true ){
    if( $default ){
        return get_stylesheet_directory_uri().'/placeholder.png';
    }else{
        return get_stylesheet_directory_uri().'/placeholder-thumb.png';
    }  
}
function wpsfi_get_featured_image_url( $termID, $placeholderSize = true, $size = false ){
    $imageID = get_term_meta( $termID, 'wpsfi_tax_image_id', true );
    if ( $imageID ) {
        $image_url = wp_get_attachment_thumb_url( $imageID );
        if( $size ){
            $image_url = wp_get_attachment_image_url(  $imageID, $size );
        }
    } else {
        $image_url = wpsfi_placeholder_image( $placeholderSize );
    }
    $image_url    = str_replace( ' ', '%20', $image_url );
    return $image_url;
}


/*

You can display the Taxonomy Featured Image in the front end using php function.

wpsfi_display_image( $termID, $size = “medium”, $class = ”, $width = ”, $height =” )
Parameters:
* $termID – (Integer) Taxonomy termID
* $size – (String) Image size
* $class – (String) Add custom class
* $width – (Integer) Width in px.
* $height – (Integer) Height in px

*/


function wpsfi_display_image( $termID, $size = "medium", $class = '', $width = '', $height ='', $placeholderSize = true  ){
    $imageID = get_term_meta( $termID, 'wpsfi_tax_image_id', true );
    $image   = '<img class="wpsfi-featured-image" src="'.wpsfi_placeholder_image( $placeholderSize ).'" alt="placeholder"';
    if( $imageID ){
        if( $width && $height ){
            $image = wp_get_attachment_image( $imageID, array( $width, $height ), false, array( "class" => 'wpsfi-featured-image '.$class ) );
        }else{
            $image =  wp_get_attachment_image( $imageID, $size, false, array( "class" => 'wpsfi-featured-image '.$class ) );
        } 
    }
    return $image;  
}
function wpsfi_get_registered_taxonomy(){
    $taxonomies = array();
    $args = array(
        'public' => true,
        'publicly_queryable' => true,
        'exclude_from_search' => false
    );
    $post_types = get_post_types( $args );
    if( !empty( $post_types ) ){
        foreach( $post_types as $key => $value ){
            // Exclude Woocommerce taxonomy
            if( $key == 'product' ){
                continue;
            }
            $object_taxonomies = get_object_taxonomies( $key, 'objects' );
            foreach( $object_taxonomies as $tax => $obj_tax ){
                if( $obj_tax->show_ui ){
                    $taxonomies[$tax] = ucfirst( $key ).' '.$obj_tax->label;
                }
            }
        }
    }
    return $taxonomies;
}


function wpsfi_excluded_post_type_list(){
    return apply_filters( 'wpsfi_excluded_post_type', array(
        'product', 'product_variation', 'shop_order', 'shop_order_refund', 'shop_coupon'
    ) );
}
function wpsfi_post_type_list(){
    $post_type_list = array();
    $post_types     = get_post_types( array( '_builtin' => false ) );
    if( !empty( $post_types ) ){
        foreach ($post_types as $key => $value ) {
            if( in_array( $key, wpsfi_excluded_post_type_list() ) ){
                continue;
            }
            $post_type_list[] = $key;
        }
    }
    return $post_type_list;
}
// Enable all Custom Post Type display Featured Image
add_action( 'admin_head', function(){
    global $wpdb;
    $wpsfi_post_type = $wpdb->get_var( "SELECT count(*) FROM `{$wpdb->prefix}options` WHERE `option_name` LIKE 'wpsfi_post_type' LIMIT 1" );
    if( !$wpsfi_post_type ){
        update_option( 'wpsfi_post_type',  wpsfi_post_type_list() );
    }
} );

Step 3: Download the Placeholder images and add to your themes directory.
placeholder.png and placeholder-thumb.png

Step 4: To show the images on frontend use this code help in category.php file or make a shortcode for category template.

You can display the Taxonomy Featured Image in the front end using php function.
/* get category id on category template */
$category = get_queried_object();
$termID = $category->term_id;
wpsfi_display_image( $termID, $size = “medium”, $class = ”, $width = ”, $height =” )

Parameters:
* $termID – (Integer) Taxonomy termID
* $size – (String) Image size
* $class – (String) Add custom class
* $width – (Integer) Width in px.
* $height – (Integer) Height in px

Done!