You can use any type of image as long as you can read in the file and create a 2d array of rgb(and alpha) values for each pixel. I am not sure about Perl's interface.

This .tgz file contains some C++ code I did for a class I took a while back used textures in BMP format. HFieldBDE.tgz

Note, the code use's VRCO's cavelibs, so it won't work out of the box, but the textures stuff is still relevant.