I don't know if an artist can know everywhere their art has been snagged. Even non-professionals can have a render or image taken without permission or acknowledgment from a non-artist venue, and used in places where an artist doesn't usually go. That happened to me. A person asked to use one of my images for their blog. I gave permission and it was posted on the opening page with credit to me. Very gratifying. A month or so later, a different person from the forum send me a message about seeing that same picture used on a completely different forum host, without reference to me or the forum admin. It was not a forum host I was familiar with. Gave me the url. Sure enough, there was my pic, without credit to me or the place it was  snagged from.  I wrote to the new forum owner but they did not deign to reply and left the image in place. The funny thing is the basic topics of both the forums were about spirituality and "doing the right thing".