...

I might be talking b**ls here, because for all I know Linux already

has

...

an open, common API to pass photos to and from the various picture editors....

I don't know of anything *specifically* for that.

However, there is an API that might be relevant here, with added

benefits.

It's a network protocol, primarily for 3D graphics collaboration,

called

"Verse":

http://www.blender.org/modules/verse/

Performance could be an issue for large bitmaps, since it's a network protocol, but perhaps an optimised version could be used locally.

This is interesting and possibly suitable. Might be more suitable as an API to interface to 3D apps (which is another area altogether - Illustrator and Corel have had good 3D capabilities for a while).

Charles