Unexplained photo on iphone

In looking over photos on my iPhone I noticed a new photo that I did not take. The photo also appears on my photo stream.

I am the only person with access to my macbook, iPhone and iPad. The passwords to my devices have recently been changed.

This is a photo of something that I have never seen before (I didn't accidentally take the photo while trying to lock my iPhone).

All other photos on my photostream/iphone have locations for where they were taken. This photo is marked as being from location "unknown".

The photo is saved as "IMG 89" and appears out of order from photos I did take (it appears after "IMG 340" before "IMG 341", both of which I did take)

Any ideas how or why this appeared?

Here's the image: