I saw a video of a cylindrical lithophane made from a PVC pipe a few years back (You tube Link).  I had always wanted to replicate it.  Not only have I replicated what was done in the video I did it with all open source software.  The picture above shows the PVC pipe lithophane I created on the left.  On the right is the same lithophane with a candle inside for back lighting.  I used Dmap2Gcode to create the g-code for cutting the image based on the lightness of the picture then I mapped the Y-axis to a rotary axis (A-axis) using a yet to be released version of G-Code Ripper.  I will post again when I finish testing and release the new version G-Code Ripper.