研究这个问题Filter For Featured Image 引出以下答案：How to hook update_post_meta and delete_post_meta?.

加上一个精细的全局变量($_wp_additional_image_sizes) 此处显示：How to get a list of all the possible thumbnail sizes set within a theme, 让我们了解捕获“的代码”；“用作特色图像”；操作单击。

该代码在每个；“用作特色图像”；点击然后，它检查并删除所有额外的图像大小，保留默认的WordPress大小（缩略图、中、大）
测试此代码throughlyGPL代码。未授予保修。检查注释

/**
    DRAWBACK
    - Setting the Featured Image can be done ONLY ONCE
    -- When first setting the FI, all other attachments intermediate sizes will be deleted
    -- If swapping the FI, the first image\'s remaining intermediate will be deleted, and the second DON\'T HAVE any additional intermediates!
    
    TODO: Restoring deleted intermediates
    - this post may have an answer: https://wordpress.stackexchange.com/a/8082/12615
*/

add_action( \'added_post_meta\', \'wpse_57369_selective_delete_intermediates\', 10, 4 );
add_action( \'updated_post_meta\', \'wpse_57369_selective_delete_intermediates\', 10, 4 );

/**
 * Catches the "Used as featured image" action
*/
function wpse_57369_selective_delete_intermediates( $meta_id, $post_id, $meta_key, $meta_value )
{
    if ( \'_thumbnail_id\' == $meta_key )
    {
        global $_wp_additional_image_sizes;

       /**
        * The global holds all additional image sizes and contains this:
        * 
           array(
           [\'post-thumbnail\'] => array(
               [\'width\'] => 1000
               [\'height\'] => 288
               [\'crop\'] => 1
           )
           [\'large-feature\'] => array(
               [\'width\'] => 1000
               [\'height\'] => 288
               [\'crop\'] => 1
           )
           [\'small-feature\'] => array(
               [\'width\'] => 500
               [\'height\'] => 300
               [\'crop\'] =>
           )
        )
       */

        // Populate a new array with single values based on the keys of the global
        $all_sizes = array();
        foreach ( $_wp_additional_image_sizes as $key => $value )
        {
            $all_sizes[] = $key;
        }
                
        // Retrieve all attachments of current post/page/cpt
        $all_attachs = get_children( array(
                \'post_parent\' => $post_id,
                \'post_type\' => \'attachment\',
                \'numberposts\' => -1,
                \'post_mime_type\' => \'image\'
            ));
        
        // Determine upload path
        $uploads   = wp_upload_dir();
        $path_pos  = strpos( $uploads[\'basedir\'], \'wp-content/\' ); // start position of the string
        $base_path = substr( $uploads[\'basedir\'], 0, $path_pos);  // path before wp-content, e.g., /etc/public_html/

        // Loop through all attachments
        foreach ( $all_attachs as $key => $value )
        {
            // This is the featured image
            if ( $key == $meta_value)
            {
                wpse_57369_delete_files( $key, $all_sizes, $base_path, \'small-feature\' );
            }
            // Rest of attached images
            else
            {
                wpse_57369_delete_files( $key, $all_sizes, $base_path, false );
            }
        }
    }
}

/**
 * Delete all custom intermediates files, except when $keep_size is defined
*/
function wpse_57369_delete_files( $ID, $all_sizes, $base_path, $keep_size=false )
{
    foreach ( $all_sizes as $intermediate )
    {
        /* We need to know the image url [0] and if it exists [3] */
        $the_url = wp_get_attachment_image_src( $ID, $intermediate );

        /* If additional image exist, go ahead */
        if( $the_url[3] )
        {
            // Path of the image to be deleted
            $url_pos  = strpos( $the_url[0], \'wp-content/\' );
            $url_end  = substr( $the_url[0], $url_pos);

            // Delete all intermediates
            if ( !$keep_size )
            {
                // loga( $ID . \' - \' . $intermediate, \'delete-me\');
                unlink( $base_path . $url_end );
            }
            
            // Featured image, Selective delete
            else
            {
                // Delete intermediate
                if ( $intermediate != $keep_size )
                {
                    // loga( $ID . \' - \' . $intermediate, \'delete-me\');
                    unlink( $base_path . $url_end );                    
                }
                
                // Keep intermediate, no action needed
                // PROBABLY, RESTORING AN INEXISTENT IMAGE SIZE MUST BE DONE HERE
                else
                {
                    // loga( $ID . \' - \' . $intermediate, \'keep-me\');
                }
            } 
        }
    }
}

function loga()
{
    // This is the FireBug FirePHP console call
    // http://www.firephp.org/HQ/Use.html
}

上载图像后的结果文件夹内容，尚未设置特征图像

设置后的文件夹内容fondo-restauraciones 作为特色图片

其他注意事项要处理所有额外的图像大小（WordPress默认值和自定义），请使用：

$all_sizes = get_intermediate_image_sizes();

/**
 * $all_images contains all intermediate image sizes, WordPress default and declared custom sizes:
 * 
    array(
        [0] => \'thumbnail\'
        [1] => \'medium\'
        [2] => \'large\'
        [3] => \'post-thumbnail\'
        [4] => \'large-feature\'
        [5] => \'small-feature\'
    )
*/