The signalstats of a single image can be calculated via ffprobe with this command:
ffprobe -f lavfi -i "movie=0000002110.jpg,signalstats,metadata=print"
I'd like to do this in a folder with sequential file numbers. In ffmpeg I'm able to achieve this sort of input like this:
ffmpeg -start_number 1036 -i %010d.jpg -vf "crop=100:100:0:0" \cropped\%010d.jpg
The filter documentation for the movie parameter implies that if I might have the right format or stream specifier things might go better.
I am able to get ffmpeg to do it with a standard -i via:
ffmpeg -start_number 2110 -i %010d.jpg -vf signalstats,metadata=print -f null -
FFProbe would be better for my target environment.