Following on from my incongruous image mapping of that tower I recently uploaded in the Image Sharing section, I decided to make a test image for image mapping purposes and then apply it to a negatively displaced crater (tower). Below you'll find my results on an inverted crater, and the settings I used to overlay the image map with cylindrical projection that best gives faithful scaling.
The scale of your image map will depend on the diameter of your negative crater, but follow the proportions I've got here and you should be ok.
ps. I'll post the test image in the File Sharing section; someone may find it useful.
John
