Hi, maybe some of you will be interested - this always seemed like something that blender should be able to do without too much trouble.
I wasn’t sure if someone else did this already, so asked on Blender-SE, but seems not.
See: https://github.com/ideasman42/batch-compo
Q&A: http://blender.stackexchange.com/questions/15755/can-the-compositor-be-used-to-batch-process-images
Command line use
batch_compo.py \
--blend=compo.blend \
--input="./images_src/*.png" \
--output="./images_dst"