You are correct. I actuall used another site as well to check. I had 1 image from some other Getty like site, I removed that one as well. After looking at the images that are listed in these companies you get a good feel if you think it is an image that would be on Getty or a Getty like sight. But I always check now.
Don't get me wrong here, I'm not trying to be an ass hat, but I think you missed my main point.. just because one of these sites did not find an image, doesn't get you in the clear, the ONLY way to be 100% certain is to have paperwork or create the images yourself. I suggest you might read the hawaiian art network posts, in regards to "free" wallpaper images.. there are also single photographers that track back their images and send out nasty grams.. I guess it comes down to if you want to gamble or not. I have since stopped using images unless I create them.
Well ... you can approach 100% certainty if you are careful, but I dont think you can ever be 100% certain.
I doubt Getty does much due dilegence to make sure their contributors are posting original material. If someone sees their work on your website, they could come after you. If one is taking comfort in the fact that you have Getty license receipts, then one should study the idemnity clauses in the license contract. I think the sense of comfort would evaporate.
Not even taking your own pictures is 100% certain. There have been cases of people losing lawsuits in which their own photo (that they took themselves) looked too much like a Getty photo. Here's a UK case I remembered:
http://www.epuk.org/News/233/getty-images-wins-plagiarism-appealI think you can even find some cases where photographers have gotten into trouble for photographing copyrighted works of art.
So, yes, if you are careful, taking your own photos is low risk in my opinion. I don't think it's ever 100% certain though.
Copyright law is outdated, lobbied and legislated to the point of insanity, and in severe need of reform, in my opinion.