I am not using my own build of jpeg.ldg for m68000 any more as there's one proven working one from OL.
Unless Olivier did the same fixes as I did, this one is proven to work under FreeMiNT+MP, not MagiC. And even if it worked for his MagiC setup, it doesn't work for yours, obviously.
Remember this is the 68000 built !!
I'd really recommend to try to build it from sources, see the email about my findings about this issue.