I picked one of my photos at random, one that is reasonably popular, and had a look at the recent stats. I should do it more often!
I learned, from the last 2 days' referrals, that it is being used as a homepage image for searchslate.com and A6.com search engines, screenshot below.
It is also featured on this list of rainbow textured photos on a design blog.
I should check my photo stats more often!