TreeBuilder is actually what I ended up doing, but it really felt and looked ugly. I'm really shocked Mechanize doesn't already do this already in its link extraction. I mean a Mechanize::Image class exists. There's no reason to "textify" anything when you could just include a reference to a Mechanize::Image object.
Thanks though everybody :)
I agree with most of you.
But what will you do? when the image in an input tag like :
<input name="image1" type="image" src="images/go.gif" align="middle" width="25" height="19" border="0">
How to extract such images?