They dont even have budget for photoshop now :(

tl;dr its looking for difference between sections of an images "error levels" which if someone modifies an image, tend to increase around where the modification happened as it no longer matches the rest of the image.

This is not a smoking gun though as it happens between different colors and contrasts, you can get a difference like this just between a dark and light object.

That said, looking at this just from the image alone its clear that the bag, the clothes on the empty chair and the mans face have been photoshopped (possibly even his hands).
The bag and clothes have different shadows between the small and large image that also do not fit with the lighting of the rest of the image and the mans face is of an entirely different quality than the image around it, the reflection is also of someone else looking in a different direction.

Generally be best way to tell if something is photoshopped is to ask "is the image horribly compressed" when things look a bit weird or off. Thats the crutch that most people use to fake an image, its a lot easier to make something look believable if the entire image is of the quality you'd get out of a phone from 2005 then having a perfectly crisp image and only the editted parts looking like shit.

/r/NonCredibleDefense Thread Parent Link - i.redd.it