preventing spam sign ups

[falsepride]

the last thing anyone really would want would be a spammer signing up 1000s of fake email address's onto their mailing list. how would one set up one of those image things, where you type in the text in the image into a form. i'm assuming you have to encode the image name, so the spammer couldn't just take a list of all the image names, and values, and easily bypass it. i have a feeling some php will play into this too, but i wasn't quite sure what forum to put this into

[Belisarius]

The term you're looking for is CAPTCHA.

There's quite an art to foiling spammers. If you're using a custom-coded webapp, you don't usually need to worry about 1000's of spammers, because they only hit A) high-traffic sites or B) commonly used webapps in large volume. That's because it's worth their time to write scripts to try and sneak through the mechanism used to keep them out.

For smaller websites, you'll always need to worry about a few spammers (we get them here on a semi-frequent basis), because a human should always be able to signup.

If you're using a common webapp instead of a custom-coded one, what I would suggest is asking a simple question to "prove" that the person registering is a human. Something like "What is the color of the sky?" Very easy for a human to answer, not something a generic script trying to get into a bunch of websites can answer.