How do you you tell if a photo is photo shop?

Answer 1

It's hard to know for sure, but here some dead give aways:

1. Conflicting shadows (say one building has a shadow pointing right but a tree has a shadow pointing left)

2. Weird colors

3. Rigid (and obvious) lines (say your friend photo shopped huge muscles onto himself, but there is an obvious border between his skin and the muscles)

4. Distorted features (odd curves or blurry areas)

5. Conflicting reflections (if there is a reflective surface nearby, check it. If it reflects something different than the photo, then there is photo shop work)

Hope this helps!

Answer 2

To know you should actually have a little Aesthetic skills.You can easily differentiate from a real and a photo that is Photoshopped.If the person have added filters and there are some dynamic lighting effects then it is obviously Photoshopped or done with some other software like Light room.Many of the pictures are not added with the effects so you can logically think that how a picture should look when it is real.In many pictures there are thing that are unreal and there are no proof of that the fact exist so that picture is a fake.You can though try to zoom into the photo near the edges where you think the photo is edited from to find the natural changed lighting.
Many times the fake photos are really difficult to be differentiated from the real one because the work is done so finely that you cannot differentiate.The work is done by a professional.