I think the authentication image you're referring to is called a "captcha". Authen::Captcha may be useful. There are tons of CPAN modules to do pie charts, like Chart::Pie. None of which I've used myself.
I've had good experiences with PAR; you don't even have to have Perl installed to run a pp-generated executable.
The BIG downside to "captcha"-like technologies is that it limits access to those who can use image-oriented interfaces. That excludes the whole blind population, or those who use text-only browsers for other reasons. (That also means the US Government can't buy or use your methods, since they can't legally exclude a disabled population so cavalierly.) Before you dismiss that group out of whim, ask yourself if there is any other way to accomplish your goals.
For every perceived problem, there is a solution that is obvious, easy, and wrong.