Thanks Andrew. I bookmarked the "14" part of the photo caption, named it "Photo14" and successfully cross-referenced it. It looks straightforward to automate that process when the photo captions are created.

I inserted another photo earlier in the sequence and previewed the document, now the "14" in the photo caption is "15" but the bookmark is still "Photo14". That will cause me problems down the track when lots of photos are inserted because I won't know which bookmark to cross-reference to. Can you see a way around that?

Also, is it possible to output a list of all the available ReferenceKind options?

Thanks for your help.