Prank photo appeared on my iphone

After completing a triathlon, the below prank cartoon appeared in my iPhone photo library. I noticed the cartoon days later, and had never seen the cartoon. I checked the browsing history, and the photo was not retrieved from the web on my phone. No one had access to my phone at the time the cartoon was saved, so I am a little worried that someone I don't know would be able to pull off such a prank. I'm worried from a security standpoint, as this phone is used for work and has a six digit passcode and thumbprint lock, it should not be accessible to anyone but me. If this picture had been of a more serious or graphic nature, I could be dealing with serious implications.