In Opera 12, hovering over a thumbnail shows the URL of the large image and selecting 'save linked content' (equivalent to save target) saves it. Selecting 'save image' of course saves the thumbnail image itself.

If you're seeing a php link, which browser are you using? It sounds similar to problems people have had trying to download a zip file from a link, for example and getting the actual file contents opening in a browser window. I can't remember what the solution to that was, maybe something to do with mime types or security settings.  

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken