Early on I switched my album art method from Folder.jpg to embedded images to be more compatible with programs and specifically iTunes/iPod.
Unfortunately I recently discovered iTunes doesn't display GIFs.
Would it be possible in future versions of MM to have it convert GIFs to JPEGs when they're embedded into the mp3? That'd be awesome.
I just confirmed that iTunes does read BMP, JPG and PNG files only, not gif.
The best option would actually be converting the GIFs to PNGs, since they are both lossless. I also noticed my 24bit PNG file didn't display properly in MM, but it was stored correctly. That's not a big issue, though.