Captcha replacement
ajax, captcha
Solution
It appears to be this one: http://www.webdesignbeach.com/beachbar/ajax-fancy-captcha-jquery-plugin.
How do you implement this?
Of course, you can implement the functionality on your own (see other answers), but this plug-in seems to be highly configurable :)
Any free library to do this?
Yup, see link above.
Problem
I stumbled upon http://www.kettletime.com.au/chance where the user needs to drag and drop a box with a number into another box to prove that he is human. How do you implement this? Any free library to do this? Thanks