I am looking to create a Blurb book, using a lot of photogtaphy with accompanying text. Has anyone got any experience with either:
a) Handling lots of photographs in Scrivener
b) Exporting to Blurb, either directly of indirectly
Many thanks 
I’ve used the Blurb plug-in that’s built into Adobe Lightroom to create three photobooks. This has been handy. The books have been predominently photographs (I’d estimate that it’s a 75/25 photos-text ratio).
Is your book going to be more photos than text? If so, I’d suggest trying the book feature within Lightroom rather than turning to Scrivener in this instance. Even if you don’t want to subscribe to Lightroom permanently, you can download a fully-functioning 30 day trial; just make sure you finish and export the book within that 30 days!