I downloaded the official Mac binaries today from:
http://www.imagemagick.org/script/binar ... php#macosx
They do not support JPEG or PNG. They work fine with GIF, but that's not all that useful by itself (:
I have verified that if I use binaries built with macports there is no problem. However I'm setting up a tutorial for beginners for whom macports is a bigger commitment... at any rate, these binaries should probably work, and right now they do not work in a useful way for most purposes.
I see threads about this going back some years now; is it a recently reintroduced problem, or a longstanding one?