Add CDN to external images in posts

[SnakeV]

I'm trying to include a CDN in all images embeded in posts.

For this purpose i have created a plugin with a simple preg_replace:

preg_replace("/<img .*?(?=src=\"http:\/\/)src=\"http:\/\/([^\"]+)\"/si", "<img src=\"http://i1.wp.com/$1\"", $this->post['message']);

My problem is that it replaces in some posts more than it should:

For example with this it replaces everything instead of just the img src.

<img src="http://www.vbulletin.com/images/smilies/spinny.gif" border="0" alt="" title="Spinny" class="inlineimg" />) <br /> <br /> example text text text


Any clearer way to do the preg_replace?

I just need to append http://i1.wp.com/ in the img src (and remove the http://) to get an URL like this:

http://i1.wp.com/www.vbulletin.com/images/smilies/spinny.gif

Thanks!