Is that a "local" directory tree? I'm thinking of running a script on the site itself...

You can use File::Find to go through the whole tree. For each file, you can use HTML::LinkExtor, or one of the other available link checker modules (I think there's even one on this site), to extract the links. Next, all you have to do is check the actual links.

If HTML::LinkExtor doesn't work, it's easy to throw something together with HTML::TokeParser or HTML::TokeParser::Simple, go through all the tags, and check the attributes for only the proper tags.

Before I go too far and do all the work myself, do check if you can make it work yourself. I'm willing to look into it, if I know it will be appreciated.