There is a patent-free 100% gif-compatible format. Here's an excerpt
from the JPEG mailing list:
Date: Wed, 4 Jan 1995 03:22:34 -0500
From: ghost(_at_)aladdin(_dot_)com (L. Peter Deutsch)
To: Multiple recipients of list <jpeg(_at_)cs(_dot_)columbia(_dot_)edu>
Subject: Re: GIF and the IJG code
I'm considering taking the following approach in Ghostscript.
Consider the following encoding scheme for N-bit binary data (let's
take N=6 for the sake of exposition). We encode N-bit data using N+1
bits for each data element, in order to allow adding two out-of-band
signals: a "sync" signal for error checking, and an end-of-data
signal. For N=6, we use the following encoding:
Data values: 0xxxxxx
Sync: 1000000
End of data: 1000001
We further require that the sync signal occur at least once every
2^N-3 elements in the data stream. (E.g., for N=6, at least once
every 61 elements.)
This coding scheme is a simple and obvious one. It isn't a
compression scheme; in fact, it makes the data larger.
Perhaps the MIME spec should simply point out that there are patent
concerns with image/gif (and LZW image/postscript). Perhaps it could
also reference patent-free alternatives that are currently registered
(e.g. image/tiff with CCITT compression schemes?)
- Chris