Right now I successfully grabbed the full element from an HTML page with this:
//img[@class='photo-large']
for example it would return this:
<img src="http://example.com/img.jpg" class='photo-large' />
But I only need the SRC url (http://example.com/img.jpg). Any help?
You are so close to answering this yourself that I am somewhat reluctant to answer it for you. However, the following XPath should provide what you want (provided the source is XHTML, of course).
//img[@class='photo-large']/@src
For further tips, check out W3 Schools. They have excellent tutorials on such things and a great reference too.