Regarding the search engines listed by Watchtower-Free:
I just took a few minutes to run a section of text from my web site through each of them. The text is out there, on the web and is indexed by search engines, so should easily have been detected by any of the software - or, for that matter, by a simple Google search. However, dustball.com and plagiarisma.net failed the test, reporting the text as accurate. Searchenginereports.net failed to complete the test, reporting an error repeatedly. Grammarly.com wanted me to sign up for a free trial of their service before providing results.
The other two services correctly identified the text as originating on my web site (www.dispelthedarkness.org). However, neither identified the text as having also appeared on JWN, which they should have, since the text was part of an article that I cross-posted here some time ago.
Even Google only brought up the instance of the text from my web site, not from JWN (it's from the post found here). So, is there really an effective online plagiarism checker that will catch all instances of a text's occurrence? If I had only posted the article on JWN and not on my web site as well, someone could have copied it and never been detected.