Captcha and Spamming

Captcha stands for “Completely Automated Public Turing test to tell Computers and Humans Apart” and is a technique commonly used, e.g., on blogs to prevent robots from comment-spamming. Blogspot has an option for “word verification,” which is an implementation of captcha.

It appears, however, existing captchas have been shown to be rather weak (see the “Defeating Captchas” section in the Wikepedia entry), but have been effective in one thing: confusing email readers’ spam filter. There has been an increase of email spams with spam content in embedded images and random words in the main text. The embedded images are “enhanced” with captcha-like techniques in an attempt to thwart OCR-based filters. See, for example, this image:


Again, the spammers are still winning the battles ...