Solve a stats mystery for me?

I have an artist site, with few enough visits that I notice the stats of which pages get looked at. Every day, there is one particular painting which always gets views. None of the other paintings is ever singled out like this one.

But what REALLY confuses me is: when I look at dashboard stats, the views for this painting show that people are looking at the attachment page. I don’t even know how it’s possible to navigate to that page from inside my site, since my site shows all the paintings in a lightbox.

How are viewers even getting to that attachment page? Is there something weird and different about the code on that painting? Or does it mean there’s some strange spam link stuck to it that I can’t see?

I’d be grateful for any light that could solve this mystery.