Reading Mac-encoded image

I received a JPEG image from a Macintosh user, sent by email, but inline. I
asked him to send it as an attachment, and he replied that his setup didn't
permit this. As a result, it is Mac-encoded: the 'file' command
outputs: "AppleDouble encoded Macintosh file."

How can I convert this image to be readable? The GIMP says it isn't a Jpeg,
because it doesn't begin with the right characters. A utility for
converting Apple's native .pict format won't look at it. It used to be
possible to set the MIME type in Eudora (for Windows), but current versions
do not have the setting - it is all supposed to be done automagically. I
recall receiving a document that seemed to be from a Mac, but the sender
had accidentally set her MIME type to Base64.

TIA,

Doug.
--
Who does the best his circumstance allows,
Does well, acts nobly; angels could no more.
- Edward Young.