Good Form Security - no CAPTCHA

Question

Is there a good method of form security that does not involve CAPTCHA? CAPTCHA is so annoying, but I need security because I am getting form spam. My form is

Answer 1

This kind of validator is cute and quick!

Obviously, you will want to display one of a many possible animal images, and the list should be randomized as well.

I understand it will only work X% of the time, but adding more options to the list will help reduce spam.