I want to protect a part of a website from bots and other automated "crawlers" with a form of human character recognition (sic).

The page can be either php or, I think, Asp on Linux. I'm assuming this has been done tons of times before and considering that I know s h i t about php, a semi-turnkey solution would be preferable

To (attempt to) clarify what I'm looking for I'll give an example:
-> The page displays a randomized prompt such as [1] [7] [0] using 3 bitmapped cells
-> The user user types "170" into an html <input ..> field and hits a submit buttom to proceed to the destination page. If the user gets it wrong they are returned to a new randomized prompt where they can try again to type in the new number <rinse & repeat until they get it right>.

I've seen this on various signup pages for anonymous web-based email accounts and the suchlike before (not that I can readily find an example to help explain my request here, typical!.

Can anyone point me in the right direction please?

While I lack any specific recommendations, be aware that some proxies may cause users grief. The one at work likes to overcache, and this has led to me getting the same image when retrying one of these things, even though the server since changed it to something else. Caching the last few for a particular issue if they hit back to retry a typo might be a good idea.

Never used it, but this PHP class looks pretty good.

i saw a signup sheet that featured a word displayed in a picture to stop automated processes scanning the email and automatically logging it.

I signed up to a picture uploading service which when I registered an email appeared which sent me to a page on the site to authenticate the registration. On that page was an image (jpeg) with a key word in it. All the page wanted to do for you to read the word and type it into a form on the page. Apparently their service had been 'spammed' whereby a bot was continually registering accounts using them to host pictures of a dubious nature. By putting the word into an image the bot can't read it.

Sorry if the first post didn't make much sense, it was written during a particularly tedious phone conference.

Thanks for the suggestion, it does exactly what I need.

It also appears to work ok through caching proxies too.