Well, you can obviously draw straight on it with GD, but you don't know where the 11 is.

Sounds like an excellent candidate for adding a feature to GD.pm, at least to convert from graph coordinates to screen coords. Just a thought, but clearly that's not the answer you were looking for! If you do get anything done, be sure to send the patch or suggestion in to the GD owner.

Another option (also untested) might be to play with the graphing abilities of Term::GnuPlot which can also be used by Math::Pari. Dunno. Just throwing some ideas out there.