[RESOLVED] Random IMG/Code generator

[FishGuy]

Hi,
I was wondering how this is done, you know sites that require you to login and next to the login requires you to copy some security code from an image that the site generated in order to stop spiders/auto password crackers busting your site.?
i.e
https://secure.overture.com/s/dtc/center/?mkt=us

if you refresh the page a different image is generated.

Is this done serverside and how?

I think something along the lines of generate a random string - stire in a variable - somehow generate image containing string - then on submit compare entered value to variable.

It is known as CAPTCHA.

I am looking at ASP>Net implementation now.

Good article found
http://www.15seconds.com/issue/040203.htm

Any other tutorials feel free to post.