The captcha system you describe is gOgle Re-Captcha:
https://www.google.com/recaptcha
It's the most common captch system I come across, so much so that a lot of
people seem to think that's what a captcha *is*. There are a number of other
captcha systems like Akismet, which don't depend on gOgle servers in any way,
most of which are much less annoying:
https://captcha.org/
> Since these CAPTCHAs don't prevent spam ...
There's usually some ability to submit data in the pages that use Re-Captcha,
but some webmasters may also be deploying them to prevent DDOS?
"my guess is that they are to improve the credibiity of analticks* data."
My understanding is that the pictures users click on while using Re-Captcha
is something to do with training gOgle's machine learning algorithms. Perhaps
the ones they use for image search, but given that so many of them seem to be
about recognising cars, street signs, and shop fronts, I wonder if the data
is being used to train self-driving car algorithms for the StreetView cars.
In other words, every webmaster who uses Re-Captcha is forcing their users to
be unpaid Mechanical Turks for gOgle :{
"*stealing that term from you"
So people don't think you're just being crude, or smearing analytics in
general (there are a number of useful free code analytics packages), it's
very important to use the full title: gOgle Anal-ticks (goOgle Analticks is
also acceptable ;)
