我认为最好的办法是allow tha admin choose the featured image 对于类别from Media Library. 这就是WooCommerce对产品类别所做的。我检查了WooCommerce是如何做到这一点的（在includes/admin/class-wc-admin-taxonomies.php中），下面是可重用代码（在functions.php或您的自定义插件中使用）。它可以与自定义帖子类型的分类一起使用。

<?php
/* Image thumbnail for category */

/* If this CPT, use scripts and styles to display Media Library popup */
function media_uploader() {
    global $post_type;
    if( \'YOUR_CUSTOM_POST_TYPE\' == $post_type) {
        if(function_exists(\'wp_enqueue_media\')) {
            wp_enqueue_media();
        }
        else {
            wp_enqueue_script(\'media-upload\');
            wp_enqueue_script(\'thickbox\');
            wp_enqueue_style(\'thickbox\');
        }
    }
}
add_action(\'admin_enqueue_scripts\', \'media_uploader\');

/*show the form field*/

add_action( \'YOUR_CUSTOM_POST_TYPE-category_add_form_fields\', \'add_image_field\', 10, 2 );
add_action( \'YOUR_CUSTOM_POST_TYPE-category_edit_form_fields\', \'add_image_field\', 10, 2 );
function add_image_field($taxonomy) {
    if(is_object($taxonomy)) // edit term not add term
    $selectedimgid = get_term_meta( $taxonomy->term_id, \'YOUR_CUSTOM_POST_TYPE_cat_thumbnail_id\', true );
    
    ?>
    <div class="form-field term-thumbnail-wrap">
        <label>Thumbnail</label>
        <div id="YOUR_CUSTOM_POST_TYPE_cat_thumbnail" style="float: left; margin-right: 10px;"><img src="<?php if(isset($selectedimgid)) echo wp_get_attachment_image_src($selectedimgid)[0]; else echo "PLACEHOLDER-IMAGE-HERE.jpg";?>" width="60px" height="60px" /></div>
        <div style="line-height: 60px;">
            <input type="hidden" id="YOUR_CUSTOM_POST_TYPE_cat_thumbnail_id" name="YOUR_CUSTOM_POST_TYPE_cat_thumbnail_id" value="<?php if(isset($selectedimgid)) echo $selectedimgid; ?>" />
            <button type="button" class="upload_image_button button">Upload/Add image</button>
            <button type="button" class="remove_image_button button">Remove image</button>
        </div>
        <script type="text/javascript">

            // Only show the "remove image" button when needed
            if ( ! jQuery( \'#YOUR_CUSTOM_POST_TYPE_cat_thumbnail_id\' ).val() ) {
                jQuery( \'.remove_image_button\' ).hide();
            }

            // Uploading files
            var file_frame;

            jQuery( document ).on( \'click\', \'.upload_image_button\', function( event ) {

                event.preventDefault();

                // If the media frame already exists, reopen it.
                if ( file_frame ) {
                    file_frame.open();
                    return;
                }

                // Create the media frame.
                file_frame = wp.media.frames.downloadable_file = wp.media({
                    title: \'Choose an image\',
                    button: {
                        text: \'Use image\'
                    },
                    multiple: false
                });

                // When an image is selected, run a callback.
                file_frame.on( \'select\', function() {
                    var attachment           = file_frame.state().get( \'selection\' ).first().toJSON();
                    var attachment_thumbnail = attachment.sizes.thumbnail || attachment.sizes.full;

                    jQuery( \'#YOUR_CUSTOM_POST_TYPE_cat_thumbnail_id\' ).val( attachment.id );
                    jQuery( \'#YOUR_CUSTOM_POST_TYPE_cat_thumbnail\' ).find( \'img\' ).attr( \'src\', attachment_thumbnail.url );
                    jQuery( \'.remove_image_button\' ).show();
                });

                // Finally, open the modal.
                file_frame.open();
            });

            jQuery( document ).on( \'click\', \'.remove_image_button\', function() {
                jQuery( \'#YOUR_CUSTOM_POST_TYPE_cat_thumbnail\' ).find( \'img\' ).attr( \'src\', \'PLACEHOLDER-IMAGE-HERE.jpg\' );
                jQuery( \'#YOUR_CUSTOM_POST_TYPE_cat_thumbnail_id\' ).val( \'\' );
                jQuery( \'.remove_image_button\' ).hide();
                return false;
            });

            jQuery( document ).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;
                    }
                    // Clear Thumbnail fields on submit
                    jQuery( \'#YOUR_CUSTOM_POST_TYPE_cat_thumbnail\' ).find( \'img\' ).attr( \'src\', \'PLACEHOLDER-IMAGE-HERE.jpg\' );
                    jQuery( \'#YOUR_CUSTOM_POST_TYPE_cat_thumbnail_id\' ).val( \'\' );
                    jQuery( \'.remove_image_button\' ).hide();
                    // Clear Display type field on submit
                    jQuery( \'#display_type\' ).val( \'\' );
                    return;
                }
            } );

        </script>
        <div class="clear"></div>
    </div>
    <?php
    
}



/* and save it */

add_action( \'edited_YOUR_CUSTOM_POST_TYPE-category\', \'YOUR_CUSTOM_POST_TYPE_extra_fields_save\', 10, 2);
add_action( \'created_YOUR_CUSTOM_POST_TYPE-category\', \'YOUR_CUSTOM_POST_TYPE_extra_fields_save\', 10, 2);
function YOUR_CUSTOM_POST_TYPE_extra_fields_save( $term_id ) {

    if ( !isset( $_POST[\'YOUR_CUSTOM_POST_TYPE_cat_thumbnail_id\'] ) ) return;
    update_term_meta( $term_id, "YOUR_CUSTOM_POST_TYPE_cat_thumbnail_id", $_POST[\'YOUR_CUSTOM_POST_TYPE_cat_thumbnail_id\'] );

}
?>

<?php
$termimgid = get_term_meta( $term->term_id, \'thamaterial_cat_thumbnail_id\', true );
if(isset($termimgid))
    echo \'<img alt="\'.$term->name.\'" src="\'.wp_get_attachment_image_src($termimgid)[0].\'" /> \'.$term->name;