I think most of us are in agreement that it is acceptable to learn from someone elses code (I still learn stuff from others code, but I never copy it, just work what I learn into mine), and it is theft to use someone else’s images on their bandwith, but at the possibility of sounding stupid, the first time I put images on one of my sites I didn’t know any better and I didn’t realize that the place I got them was serving them. A friend of mine noticed it and explained to me what I was doing, and fortunatly I was able to take them down before anyone noticed. Now I would never do anything like that, because I understand and think it is theft.
All I am saying is, I would send a simple email explaining what they are doing and ask them to stop. If they don’t, then by all means change the images 
Not everyone is doing something evil on purpose. There are thousands of people drawn to the “easy money” of the Internet every day and some of them are just ignorant of what is right and wrong.