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

I dont think we can differentiate in original and fake pictures
online, its completely impossible to differentiate online.

I am a designer. Part of my work is  putting one image into another
image, to make it look real. I can tell you what are the challenges in
my work, and those are the things you should be looking for to
identify fake image.

First, the greatest challenge is the lighting  condition of the two
images are usually different. For instance image A is taken at a sunny
day, while image B is taken at a cloudy day. I will try to do my best
to adjust the lighting of A to match B, but most of the times, it
won't be a perfect match.

Second, the edges. The natural edge of a certain figure in photo is
always ambiguous. It is neither a clear edge, nor a fuzzy edge.

Third, image resolution. When bring a low resolution image into a high
resolution one, image will be seen blurry.

These are the technical challenges that are hard to work around. So
look for those to identify a fake image.

but sometimes,we can't distinguish the fake photos and the real photos.
it't hard for us to do this.
yes?