> This makes sense. So much so that perhaps it could be added to the
> core spec-tpd.tex file.

I think it would make more sense for conTeXt to first convert an image's extension to lower case before trying to figure out rule to apply.  Otherwise in order to be correct, you would need an entry for
"Jpg", "jPg", "jpG", "JPg", "JpG", and "jPG" -- not even counting the permutations for "jpeg".

> You could consider using a case-insensitive file system to store
> your data on, and lowercasing all entity input to ConTeXt, but
> that is more clumsy than the extra \definefileinsertion-s.

I don't think a case-insensitive FS is going to be an option for us (*nix only).

Back to my original question, should "\externalfigure[MY_FIGURE.JPG][type=jpg] work?  Or am I misunderstanding the meaning of the type parameter?

Cheers,
Mike