For questions about the CAPTCHA used on Stack Exchange sites to verify that you're a person and not a spam-bot.
CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is an anti-spam measure to prevent or reduce the effect of "spam bots" submitting junk to the site by presenting a problem that is easy for a human to solve but difficult-to-impossible for a computer. Some common methods are identifying "squiggly" letters, reading numbers from a slightly blurry photo, identifying an animal in a photo or drawing, simple arithmetic, and so on.
This tag is for questions about the CAPTCHA used on Stack Exchange sites.
For more information about use of Captcha in Stack Exchange network see: