Is there a reason for sites to ask for another CAPTCHA verification when some other part of the registration form, e.g. the username, was invalid?
What type of captcha will you recommend? I am looking mainly at usability, ease of use (development too), relatively secure Usability I find that those captcha with very curly words/numbers are ...
The Asirra project is a Captcha alternative that shows you pictures of kittens and puppies to fend off bots and prove that the end user is a human. Is anyone using Asirra (or something similar) in ...