This picture is better known in the anti-spam field as a CAPTCHA (Completely Automated Public Turing Test to Tell Computers and Humans Apart) - nice and succinct...
The purpose of this picture is to prevent spammers from using programs to automatically create accounts to send spam FROM before they can be blocked by Live anti-spam programs.
Now - some bots can crack through this system in under 6 SECONDS - incredible!
Spammers put this bot on unsuspecting user's computers (this is why you should use a good anti-malware program) - so that the infected computer will continually create accounts to spew spam.
The technical write-up was done by websense - its good - with pictures and everything :)