In Harry Potter, Harry had no idea about the wizarding world until Hagrid came to get him. Since he was sent to the Dursleys as a baby, how do the other witches and wizards know what he looks like when he shows up at Hogwarts, and the Leaky Cauldron? It couldn't have been his scar, because in the Leaky Cauldron, everything was dark, and Harry had his bangs over the scar. In fact, Harry always had to lift up his bangs to let people see it.
"He pointed at Harry's forehead. Harry pulled back his bangs to show the lightning scar."
(Harry Potter and the Philosopher's Stone -- chapter 6, page 99)
So how did the wizarding world know what Harry looked like before he knew about wizards?