Art theft

I am noticing this again, not using any usernames but as far as I can tell a user is taking peoples art off the internet and posting it here as if they drew it themselves. this seems to come and go as an issue talking watermarks and signatures of, and if its a younger person they don't take them off at it gives it away. it makes me really angry that that happens! art is expression of someone else, some people just need to learn.