Please consider allowing jpeg-compare to take two (instead of one) uncompressed PPM images.
This would make it much more flexible and for comparing other image compressors.
Both arguments to jpeg-compare can now be PPMs and, even better, jpeg-compare now auto-detects file types. So you can simply call jpeg-compare 1.ppm 2.ppm without any further options.
Please consider allowing jpeg-compare to take two (instead of one) uncompressed PPM images. This would make it much more flexible and for comparing other image compressors.