Determine how well the cropper is working

[misaugstad]

As @jonfroehlich mentioned over email, we need a way to evaluate how well the cropper is working. I know that we've had issues with it in the past, and I honestly do not think that they have been resolved, and I expect there to be issues with the cropper. This determined whether or not we are even training on valid data.

Some relevant issues are sidewalk-panorama-tools #8 and SidewalkWebpage #2485.