I just want to remind you, that although your intentions are good, there is potentially a HUGE flaw in the way you are going about it.

I have created an application exactly like you are doing, yet it doesn't check watermarks, just downloads files from pages and spiders out.

The problem is, on my computer, even with a high speed connection, I am only about to pull in about 5000-15000 images an hour. Now, that sounds like a lot, but look at how many images are out on the Internet. Millions, possibly billions. Think about how long it would take to spider the Internet and download each one to check for copyright infringements.

Google has a huge (thousands) farm of computers that spider the internet. If you are going to run your app constantly, you might want to get a good farm of computers if you want to do this effectively.