strange photos in iphone camera roll

iPhone 4. Today a bunch of photos that look like they were taken in China (pagodas, with oriental writing on them) appeared on my iPhone in my camera roll. I have the latest firmware and software. I have never had my phone jailbroken, and I bought it new from O2 (UK official supplier)

The only thing I can think of is that Bump was recently updated, and I was in a lecture about going to China with the computer school today. Is it possible that these photos have been transferred from someone else's phone to mine without me knowing it? (having said that, none of these photos were shown in the lecture.)