How can a person differentiate between 'original and fake photos' in a website?

There are a couple of ways for a layman to do this. They rely on what
I call consistency. Basically, among many shadows in the picture, do
they all point the same way? Is the basic levels of contrast and tint
the same throughout the photo? If not, you could be looking at a fake.
If these things are "correct", you *may* still be looking at a fake,
albeit a more artfully constructed one.