Thanks jmanning2k for your answer, but I've already deleted "my own" GD.pm, and removing the use lib line doesn't help.
Now about this: "Odds are, you didn't build it with jpeg support when you installed your own version (or didn't upload the autoload and non-native perl bits for the proper arch - FreeBSD)". Part from being able to upload the GD.pm file, can I actually upload and build gd myself?!