a function to replace image URLs into <img>

gistfile1.txt

function embed_images($content){
    return preg_replace('/(https?\:\/\/[a-zA-Z0-9\-\.]+\.[a-zA-Z]{2,3}(?:\/\S*?)?(?:[a-zA-Z0-9_])+\.(?:jpg|jpeg|gif|png))/i', '<img src="$1"/>', $content);
}
add_filter(the_content', 'embed_images');