在库短代码处理程序和输出之间设置自定义函数。抓住img 元素并添加静态计数器。然后将gallery输出返回到WordPress。

示例代码：

add_action( \'after_setup_theme\', \'wpse_74492_replace_gallery_shortcode\' );

/**
 * Replace the default shortcode handlers.
 *
 * @return void
 */
function wpse_74492_replace_gallery_shortcode()
{
    remove_shortcode( \'gallery\' );
    add_shortcode( \'gallery\', \'wpse_74492_gallery_shortcode\' );
}

function wpse_74492_gallery_shortcode( $attr )
{
    // Let WordPress create the regular gallery …
    $gallery = gallery_shortcode( $attr );

    $gallery = preg_replace_callback( \'~<img~\', \'wpse_74492_gallery_callback\', $gallery );

    return $gallery;
}

function wpse_74492_gallery_callback( $matches )
{
    static $count = 0;
    $count += 1;

    return "<span class=\'gallery-number\'>$count</span>" . $matches[0];
}

.gallery-number 
{
    position: absolute;
    left:0;
    top: 1em;
}