I am excited to announce that I have discovered that one of my photos was used in a book, Frommer's Far & Wide: A Weekly Guide to Canada's Best Travel Experiences! I found out about it in the photo credits through a Google search.
The annoying thing is that I don't even know which photo they used! However, based on an analysis of my sales, this photo seems to be the most likely one. I sold a P-EL license of this image, but what confuses me is that the sale was around the time they published the book. And the book probably had been in the design process months prior. Maybe they purchased the photo under a RF license for the design process then repurchased the photo when it was published.
I just sent an email to the publisher requesting the page with my photo, but I don't know if they'll send it to me.