How is this done?

[carlg]

I don't even know what it's called, but it's a common thing.

 

I you ever listed something on craigslist or some web forums use this before you post.

 

It's usually  some some with the background as some sort of picture.

 

For example, if you list something on craigslist you will need to enter a verification code into a text box before you can list.

The code will be some text with a picture background.  If you can't type the code properly, you don't get the listing.

 

How is this done?

 

Thanks

 

Carl

 

[BlueSkyIS]

it is called CAPTCHA.

 

http://en.wikipedia.org/wiki/Captcha

 

you may want to check out http://www.phpclasses.org/ for some pre-written, or search.