I'm in the same boat as ThirdRoulette. Before I even really got into the internet art scene, and a friend introduced me to RP (iirc it was a Naruto RP site), it was pretty much a necessity to have an image for your character - and this was when I was in middle school, so more than 10 years ago (so my details may be a little fuzzy) but at the time I hadn't ever considered it to be a form of claiming somebody else's character as your own, simply having a visual reference to go off of - but in most cases (at least what I still can pull from memory) the written descriptions would maybe match hair or eye color (sometimes both) but a lot of the details differed from what was actually in the image. And even back then I would still make characters myself and draw them, so I had used a face claim once or twice but moved on to drawing my characters myself because I wanted everybody else to see them the way I saw them, and I didn't put much thought into the concept of a face claim until recent years.
That said, I think part of the problem and the reason this is such a huge thing is that people want things to be quick and easy. Instead of having to rely on written descriptions, people want to be able to pull up a picture. I've seen it a lot where face claims were more or less required, you had to have some sort of image instead of going off of just a written description because gods forbid somebody actually has to read your character's bio before roleplaying with you (again, quick and easy) and it's kind of... ridiculous that the culture got to that point at all.
HOWEVER, on the more "reputable" sites I've been on (where I still wasn't using them myself) it was always required that you credit the character and creator of said character whose images you were using. And while that still doesn't make it okay, it's a step in the right direction. Wherever it came from, it's something that shouldn't have been a thing in the first place? Going back to the days of D&D, a tabletop RPG, all you had were descriptions and those weren't even always going to be written down. Stats, maybe, but you definitely didn't have images of your characters, and you wouldn't have just plucked an image off the internet and said "hey this is my character".
Even if there's no ill will or intended harm, it's important to realize that a character's design is pretty much always intended to be a certain way because of various things - story, personal connection, etc, and it's really.... uncomfortable to see people taking it and running with it without even giving a second thought. It's one thing to ask somebody to use a character's image as a visual reference for an RP character (which, if asked I would still say no because they are still my characters).
I think it would be one thing to, say, describe an aspect of a character's appearance and to help with the mental image say "like this aspect of x-character from y-creator/series'" with an image attached, but just grabbing an image or several images of a character and saying "this image is exactly my character" is just weird to me??