http://Бла-Бла.Ню/wp-content/uploads/2015/10/2015-10-06_12-19-311.jpg

<img class="" width="250" height="250" alt="" src="http://Бла-Бла.Ню/wp-content/uploads/2015/10/2015-10-06_12-19-311.jpg">

function my_img_replaсe($content){
$regex = '~(?<!src=")(ht|f)tps?://[w%#~:;&=+,(.(png|jpg|jpeg|gif))/?-]+~is';
$replace = '<img src="\0" class="" width="250" height="250" alt="">';
return print preg_replace($regex, $replace, $content);
}
add_filter('the_content', 'my_img_replaсe');