I've used a lot too. It should be OK to use these sites, but it was alarming to be alerted to the problem. I think this is rare, but I'm going to be using my own pictures going forward. I like to think in most cases, if you're a victim of an illegal upload, a take down notice would suffice, but it's hard to know. The majority of cases were about improper attribution. So hopefully if your attribution is good, you'll be OK.