Copyscape is one of the more popular plagiarism detection tools that helps you identify other web sites that may have copied your content without permission.
Simply enter your web address and Copyscape will try to find other pages on the web that have either lifted your content verbatim or have modified it slightly to make it look original.
The free version of Copyscape however offers only a limited set of features and you cannot perform more than a couple of scans per month (they mostly restrict queries based on your IP address).
Check for Online Plagiarism with Blekko
If you have been looking for some good alternatives to Copyscape, meet Blekko. This is actually a search engine but you may use it for plagiarism detection as well. Here’s how:
Once you are on Blekko, enter your domain name followed by /domainduptext (example). You’ll then get a list of other web sites that may be duplicating your content by scraping.
www.labnol.org <span style="color: #ff0000;">/domainduptext</span>
The /domainduptext command will detect instances of duplicate content for your entire domain but you may also use Blekko to find duplicate copies of individual URLs. In that case, use the slash tag /duptext and replace the domain name with the full address of a web page (example).
http://www.labnol.org/internet/print-from-mobile-phones/17827/ <span style="color: #ff0000;">/duptext</span>
Obviously, not every website detected by Blekko may be plagiarizing your content but it can still help you discover some new culprits.
Web Pages with Duplicate Content
On the topic of scraping, Google says that it is unlikely that duplicate content “will negatively impact your site’s ranking” but you can always file a DMCA request to claim ownership of the content and request removal of the other site from Google’s index.