"""True, but at the same time you shouldn't be hosting your pictures on the internet where anyone can copy it if you want to charge money for it. """
This is "blame the victim". Posting something on the internet does not make it public domain.
"""If I was to place some proprietary code on a public git, or just display it on my public webpage, should I get angry if people take it and don't pay me for it?"""
Yeah, you should.
It's the same if you posted some GPL code on a public git, and someone took it and build a closed system with it.
In both cases, the creator/owner or something did not have his wishes and copyright respected.
The same way we insist on people/companies respecting GPL copyright licenses, we should respect other people's licenses for THEIR stuff.