Eric Howe created some nice tools to convert common graphic formats to ImageViewer and PBM format. You can find more about this tools at his Pilot Page. Download ready to run RPMs for S.u.S.E. Linux:
Palm Pilot prc-tools
pbitm to PBM converter
pbitmtopbm-1.3-0.i386.rpm pbitmtopbm-1.3-0.src.rpm
Palm Pilot Image Viewer
to PGM Converter
imgvtopgm-1.3-0.i386.rpm imgvtopgm-1.3-0.src.rpm To view the images on your Pilot, you can use TinyViewer by Ken Shirriff.
There are lots of images to download at MemoWare.