Isn't this what plagiarism algorithms are doing? Scrape the content, run through the plagiarism filter (although not a very strict one to prevent false positive

Isn't this what plagiarism algorithms are doing? Scrape the content, run through the plagiarism filter (although not a very strict one to prevent false positives on quotations and the like) and you are done. If there's a match, show it so the submitter can see for himself.