Form submission on web - image containing characters for user to type in

Question

Often when you fill in a form on the web you are asked to type in some characters from an image to validate you aren't a robot etc.

Does anyone know A) what you actually call these things? B) are there any third party tools that can be used to generate the images? (.NET focus here)

Answer 1

Captcha

The term "CAPTCHA" (based upon the word capture) stands for "Completely Automated Public Turing test to tell Computers and Humans Apart."

Re-Captcha is very popular

Answer 2

A) Captcha
B) ReCaptcha

Answer 3

This is called Captcha

http://en.wikipedia.org/wiki/Captcha

Answer 4

Note that Recaptcha has an ASP.NET implementation, which you should find useful.