The rather heavy imagemagick program is used to:
apparently it can't copy the metadata from the tiff to the jpg file, so the perl program exiftool is used for that.
It would be nice to replace all that with a lightweight and fast program.
Ideally it'll be replaced by a tiny program that uses libtiff, libjpeg and libexif2
Instead of libexif2 you could use gexiv2, it's an GObject wrapper around libexif2. Perhaps that's easier in an GTK3 program.
Issue now tracked here: https://gitlab.com/postmarketOS/megapixels/-/issues/11