I did some quick research a while ago and some of the online hash calculators that come up in google are affiliated with one of the online hash crackers. That was the main reason I made my own hash calculator page -- so I could create hashes easily without worrying about the preimages being remembered. So you are right to be concerned.

I tried to think of a way you could test it for yourself, but for everything I thought of, I also thought of a way I could easily pass the test while still adding the preimages to the database. So for now you'll have to trust that I'm not, or use a different hash calculator.

Here's the source code for that checksums page if you want to run it on your own:

http://pastebin.com/tH6EVxR1