Change img scr path but not filename in a post body

I need to change the src path (not necessarily http for all img in a blog post body.

I prefer to use preg match / replace if possible

For example:

<img src="b.image.com/kittykat.png" />

would become
<img src="/images/kittykat.png" />

Code (markup):

 

$string = ' <img src="b.image.com/kittykat.png" />';
preg_match_all('/(src)=("[^"]*")/i',$string,$matches);

$src = explode("/",$matches[2][0]);
echo '<img src="/images/'.$src[1].'" />';

PHP:

 

Or you could just get it in one go:

$string = ' <img src="b.image.com/src/kittykat.png" />';
preg_match('/src\=[\"\\\']{0,1}.*?\/([a-zA-Z0-9\_\-\+\s]+\.[a-zA-Z]+)[\"\\\']/i',$string,$matches);
//$matches[1] contains the filename

PHP:

 

This definitely works but I can't see how to use it to modify my database fields (the posts).

I think I need to match everything before the filename not the filename so I can you preg_replace

right?