Use embedded preview from raw image rather than converting the raw
This is a patch for #413. Not really applicable, but perhaps some would like to have it as an option.
Something like this would be very useful indeed! I would prefer to avoid dependency on external tools though, and I think there is a pretty good Python alternative: https://github.com/letmaik/rawpy rawpy is based on libraw so it supports a wide range of raw formats (CRW/CR2, NEF, RAF, DNG, and others), and the README has an example of how to extract the preview image.
I'd like to retire this PR. I have restructured my archive so that the public part only contains JPEG images and all raw images are in my internal archive. So I don't use it anymore.