I don't care if people lie about their techniques, personally. They obviously have a reason for it, whether it's because they feel inferior for using what some would call "cheats" (and the whole concept of "cheating" at art is a silly one to me), or because they feel possessive of their methods. I know a lot of younger artists will post pictures and say "don't steal my style!" or words to that effect, trying to keep themselves uncopied. Maybe some people never grow out of this mindset. It could also be that sometimes an artist doesn't feel like going over every single little thing they do, or else forget some things they've done. I know it's not uncommon for me to forget completely how i did a picture a week after finishing it. There may be malicious intent, but i think usually without some kind of reason, most people wouldn't lie to others to hurt them intentionally. The majority of people tell lies to protect themselves or others.
I don't think you're necessarily wrong
to be upset about people lying, as long as they were lying to you or affecting you in some way. But i can't understand
being upset about it. If there are such obvious ways to tell how someone did a painting, who cares if they lie to you? I could only see it mattering if you hadn't heard of the technique they used or something. And while it's nice to hear from artists you admire what methods they use when working, there are HUNDREDS of others out there that actually are giving away their techniques through tutorials and works in progress. It's not exactly like the internet is hurting for instructions on how to work in just about any method - certainly enough for anybody to get started toward developing their own techniques and tricks.
It doesn't seem productive or useful to argue with them about their techniques though. The fact is, unless you were sitting right there watching them paint for every second they were working, you
can't know with absolute certainty whether they used a photo for reference, painted over it, created it from memory, or what. Some artists really are so good that they can paint realistically without tracing a photo. The only thing "calling them out" does is cause anger, bad feelings, and resentment, as well as smear the person's image in the eyes of people who view their technique as "cheating", even if they used their own photos. It seems to me the only ones who are "spiteful and lacking integrity" are the people who smear someone's image by "calling them out" publicly.
Now, if they're breaking copyright law, the correct thing to do is politely email them about it, and if no action is taken, to notify the person hosting their images of the violation and send proof. Making a big public fuss out of it is childish and unprofessional.
I don't know what tell-tale signs you're talking about finding in Photoshop to spot a photo paint-over, but if you mean that stuff about how the different parts pixelate differently, you need the original
photoshop file or some other uncompressed, lossless file format to see that . A compressed jpg at web resolution will always have some artifacts and funky pixelation in it.