用php附加图像

I'm working with a plugin that lazy loads images http://wordpress.org/plugins/unveil-lazy-load/

  if(is_feed() || is_preview() || self::is_smartphone())  return $content;

  if ( strpos( $content, 'data-src' ) !== false )
    return $content;

    $dummy_image = self::get_url('b.gif');

    $content = preg_replace( '#<img([^>]+?)src=[\'"]?([^\'"\s>]+)[\'"]?([^>]*)>#', sprintf( '<img${1}src="%s" data-src="${2}"${3}><noscript><img${1}src="${2}"${3}></noscript>', $dummy_image ), $content );

    return $content;
}

From what I gather, this is checking to see if content 'data-src' exists and if it hasn't loaded, it appends the source with 'b.gif' until the data loads then lazy loads the image.

Using this line:

 $dummy_image = self::get_url('b.gif');

I'm looking to append the image with and actual so I can add a class to a preloaded image instead.

Any suggestions would be helpful.