How can we differentiate edited photos with original photos?

you can't easily spot an edited photo from a real one, especially if the editor is so skilled that he makes his work flawlessly. but you could always try to check it by using an editor, when you zoom it, you'll usually see flaws (like areas that are too smooth, not evenly blemished out or something like that) sometimes, you'll see creases too,,

Look out for blurry lines, pictures which do not blend well and skin tones which don't quite match. Check out face and neck areas and stuff like that. However, I do agree that there are really original looking super imposed pictures which are hard to detect.

There are two things to consider. One is the lighting. If the light source does not match the direction of the light then that is fake unless it was the idea of the photographer to use special tools to manipulate the lighting. Another thing to consider is the pixelation. If a portion is blurred in the picture while the surrounding pixels are sharp, it must be edited. I use that technique often and I'm trying to learn how to manipulate pixels without blurring it. Another thing to look out for is the proportion. If a man is small in comparison to an environment then it may be because it was edited. Also, If a man's head for example is too big for it's body then that may also be edited. Remember that a picture may just be naturally blurry, unproportional or have a lighting that's off but that doesn't mean it's edited but these are the common mistakes of people who like to post-process so keep an eye for these :D