That's an image, not an imagemap. An imagemap is a list of shapes defining the mouse-clickabable areas of an image. Maybe you should have read up on get_hotspots in the GD::Graph documentation before declaring it irrelevant.

And the OP is correct, it's not supported by bars3d. I looked at the source code. bars sets $self->{_hotspots}->[$ds]->[$i], but bars3d does not. The newest GD::Graph3d is 4 years older than the newest GD::Graph. Hotspot support probably didn't exist in GD::Graph back then, given that it's currently in beta.