I agree with anya_sf! I can think of a couple of additional situations for which it'd be nice to be able to post a photo without having the book/recipe on ones Bookshelf:
* Recipe reprints in magazines and newspapers. I have a stack of clippings from which I periodically pull a new recipe - a bunch are reprints from cookbooks vs. recipes developed by the newspaper/magazine staff.
* Online recipes which aren't in EYB (e.g., a number of personal blogs) but which clearly cite a specific cookbook as the source of the recipe. And for online recipe sources indexed in EYB, it'd be nice to cross-post the photo with the original cookbook.
Updated post: Just saw that I posted this while you posted your response, Jane. Thanks for the explanation!