Terminology for fake photograph
You can say that the photograph has been doctored if it was changed to deceive people.
Normally if a photograph has been faked it is said to have been Photoshopped, or called a Photoshop, after the popular image editing software.
Sometimes this is shortened to shopped or shop, as in:
That photo's a shop [or been shopped], I can see the pixels!!1
More general terms include forgery, counterfeit and of course fake.
It would be perfectly legitimate to say such a photo was a forgery.