Two good reasons
There are two good reasons to believe these "Panther Screenshots" are fake:
Arn doesn't buy them.
Apple legal has not come to crush the rumor and pull the images.
Remember the prelim MMD schematic? The heat came fast and furious on that one.
True hardware rumor test:
If it is a major renovation or new product that Apple wants to keep the element of surprise on, then expect to--
a) see hastily leaked documents illustrating the item, and
b) MINUTES later, not hours or days, said documents or images being replaced by Apple legal disclaimers.
If an image or alleged internal document is bantied about for a week on the rumor sites, it's likely a fake.
Rule of thumb: if a rumor looks juicy, save any related sites to your HD. If they are pulled 10 minutes later, you've got a winner...