>>Whenever someone alters an image, unless they are pixel perfect in their work, they always leave behind indicators that the photo is modified.
Most digital photos these days are manipulated, heavy use of filters, cropping, some cut and paste or shadowing. Supposedly they were going to stop giving Pulitzers to digital photographers.
None of this addresses staged photos (think of the shot of 20 photographers getting a closeup of the Palestinian woman crying at the “wall” while her son giggles at all of the attention the press is giving.
None of this addresses misattributed photos (the 2014 photo of child abuse under President Obama or the protester’s photo of is kid at a rally behind “bars”).
Excellent points
As in:

That kid is in the lower right, behind the kid in the red baggy pants, of the last photo.