Alternative captcha ideas for future

Submitted by n8coder on Tue, 05/19/2009 - 16:12

Now there are multiple captcha types against spam/abuse:

image captcha
ascii captcha
audio captcha
math captcha
easy questions

How will next generation captchas look like? I think in the future there will be much more captchas types like:

car captcha
film captcha
famous people
famous places
number to text
word suggestion with add remove extra letters(ie: gogle, new yoork)
animals (ie: which animals do you see in this picture from left to right)
traffic captcha

What do you think what more could be one of next spam-preventing technologies?