which is why you don't see it on every Web site. Even asking a simple math question, that's not fool proof either. Anything related to asking a user to do something that might be difficult for a computer to do, will be somewhat difficult for a user. Depending on your spam amount and your Web site audience, you might want to check if they are using certain computers, whether certain fields are filled in correctly, whether they have JavaScript installed, whether they've been to a Web page prior to filling out a form, etc. There are certain trademarks users will have that computer by themselves will not. If you can make a list of those marks, you can use those to reduce the amount of spam you are receiving.

~Sovereign