Sharing photos from network share?

I have the Gen-2 Apple TV. Home sharing seems to be working OK from "my" iMac - that is, I can see music and movies in my library. However, I'm unable to share the photos I want to show on the TV.

"My" iMac isn't used for iPhoto - we have another Mac that does all that - but I have a network file share (AFS from Linux) which has all my photos on it. All I want to do is select a folder on that and share those photos to the ATV. (This same folder works fine as a source for the Mac's own screen saver.) In iTunes, when I go into Advanced->"Choose Photos to Share", "Choose Folder", and navigate to the folder I want to use, it tells me how many photos are in it - but on the ATV when I go to the Photos selection, it tells me that I need to go use "Choose Photos to Share" to select what to show.

I've searched these forums and the web at large and I can't find any discussion of this being done (successfully or not). Am I missing something? Is it actually not possible to share photos that aren't locally stored or in an iPhoto library? If so, that would be most unfortunate.

Thanks in advance...