People are shit at judging their own smiles.
People often think photos of themselves where they’re smiling in a stock-photo style are the ones where they look best, but they’re not. They’re the ones which are least reminiscent of that person actually looking happy. Left to their own devices, most people’s favourite photos of themselves are ones where their smiles look forced and weird. That’s because people don’t actually see their own face very much, so they’re not as familiar with its nuances.
It’s great seeing a photo of someone you know with a big and real smile on their face, because that’s the face that you associate with them being happy.