Plagiarism

Hi i was wondering is there any computer forensic method of detecting material printed in a document (say a word doc) from the Internet?
I know about the Google API and how to use quotation marks on google also. I was just wondering if there are any forensic methods that might be out there that i'm not aware of.
I was thinking say for example you have evidence within your document and you want to figure out where on the WWW that text came from?

I'm aware of commerial software out there that can detect plagiarism / collusion. I'm just wondering if anyone knows of any other methods out there / you know of.

thanks in advance.
-Rick