I recently figured out you can actually do a google search of your images to see what turns up elsewhere online.
On google, go to google images, and drag or copy one of your images into the search bar. It will then search for the image online, and come up with similar images as well. I did not know this was possible before, and it gave me a good idea of where my images may turn up.

I will always ask before using other people's images. I am in two minds about people using mine. I would prefer to be asked and credited. However, I understand that that is not how things work in everyday online publishing today. I will not get annoyed if I find my pictures elsewhere, unless there is an obvious commercial interest to using it.

I have had someone copy a complete bead business concept from me once. It was a bead subscription with monthly packages. They had actually copied content from my site. I contacted them, and they took it down immediately. Not too long after I stopped this business, someone else popped up again, clearly 'inspired' by my work. I decided not to get into it. Could not be bothered, but still at the very least incredibly rude, if not illegal.