I think placenamehere maybe on to something. I've wondered about why facebook couldn't find a photo on my pages to show as thumb when I tried to link to my galleries here.
Showing a simpler pages, with direct display of images, to spiders and scrapers, may be the easiest way to do it. But it may be a good idea to discuss it with google, as they aren't to crazy about presenting them with a different page when normal browsers get. But it should be okay, as long as the contents is the same. And is doesn't have to be pretty, as nobody will ever see it (unless they choose "show cashed" in google).
I've joined zf for two things (about five minutes after the announcement of the photobox print service): Private Events (weddings etc) and Public Events (concerts etc). Search Engine indexing is not an issue with Private Events, but for Public Events it's crusial.
I can post links to the Public Event galleries in all kind of places, but most people will simply go into Google and search for "faith no more roskilde photos". There where my gallery of those photos needs to show up...