Do you think about how a picture or other item came into your possession? Did the person who gave you the image really know who it was? How was the picture or other item identified? Just because someone on the internet said it was a picture of your great-great-grandpa does not necessarily mean that it was.
Most of the time things things are right, but occasionally errors are made. At least give a moment's thought to the possibility that the picture might be labelled incorrectly.