As a start, I'd suggest taking a look at the Graphics section of CPAN. Perhaps the most widely used module is GD, which is a Perl interface to libgd, a graphics library that can create and manipulate images in PNG format. You can use the Perl GD::Graph module to make pie/pizza charts.

GD is quite flexible, in that you can compile it with support for JPEG, and with support for rasterising TrueType fonts into your image, if you've got the appropriate libraries installed on your system. ActiveState also offer pre-compiled binaries of GD for ActivePerl on Windows.

I haven't used it, but the Imager Module, also on CPAN, seems to have some features that GD doesn't have - any other folk on here got experience with using it?