An alternative to a CaptchaTest.

In a CaptchaTest, you add something like an image, and ask a person to read it and place in the answer.  Increasingly this is ineffective, because:
* computers are increasingly able to beat them; and
* labour in some places (Russia, India, China) is cheap enough that the nasties can simply pay people to do nothing all day but solve the ones they can't crack.

So, another possibility is the AntiCaptcha.  Instead of asking for a human to solve some puzzle, you generate the image and leave an input box, preceded by the human-readable instruction to "leave this field blank".  Any contribution which includes content in said field is silently ignored.  As it happens, this is also great for testing whether or not your visitors are able to read.