I don't get what you mean by "doing that for every image", but yea, I'd probably use Assets for that as well. You asked for a solution without Assets and said you are "doing it on the html that gets returned", though.
Note the function you're attaching to each element can be the same function every time again, if that's what you mean. You could save a reference to both that function and the Request.HTML instance, and re-use them. Whatever works best for your situation.
