You can give a digital photo just about any film trait in Photoshop or other digital post processing software, on a computer screen it is rather hard to tell one from another with just straight color or B&W photos. It gets easier when someone tries to get artistic and fake a print process that requires making their own paper or something like that, then you look for the errors in process to be exactly the same on several photos. I have seen fake Polaroids, fake sprocket holes, fake van dike brown, fake cyanotype, fake tin type, and it goes on.
With prints you can hold, touch and see, you can tell a fake by just looking at the back of the paper.
I have made fakes on the computer a bunch of times mostly because I can not yet tell what something might look like just by looking at a negative, so I will scan the negative and then look at it in several processes before deciding what process to use to make a print. I would never try to pass off one of these fakes as the real thing, but I do like having the ability to make them for testing purposes.
