I need a utility with which to compare pairs of images.

In a first step I would perform a batch RAW conversion of a large number
of images, then I would compare these images with images I converted
from RAW to JPEG some time ago. I would of course use the same RAW
conversion parameters I used when converting the first set of images.

I forgot which images received some editing after the RAW conversion, so
the comparison result should be a number or something else telling what
the difference between the images is. Differences could be:

1. slight differences caused by a different JPEG compression level
2. slight differences caused by a different version of the RAW
conversion software
3. local image retouching (i.e. editing away of distracting image
elements)
4. larger changes

I would like to be able to detect differences as of 3. and 4. and ignore
differences as in 1. or 2.

This software would probably calculate the difference between the two
images and then apply a function to evaluate the difference image.

The software should be command line so that I could run it in batch mode
with a script or a software which can operate in batch mode. The output
should be stored in a text file. Any suggestions?