I would be willing to bet that if you had a sim whose grandchild, or perhaps even great grandchild was named after them, the picture would occasionally oscillate between the thumbnails of the younger and the older. Or they might just be leftover remnants in RAM. Maybe if you restarted the game or your computer they would go away. as I recall, when Mortimer in my game turned into a teen, and subsequently into an adult, his picture would often revert back to when he was a child. This stopped the next time I loaded up the game.
My adult Mortimer's thumbnail is constantly reverting back to childhood, and Bella does it occassionally too. Restarting the game/computer has no effect.