My step sister used to have a whippet who would curl her front lip up like a snarl to smile at you like a person. If my shar-pei used to do that it was a threat like it is in wolf language. A dog pulling what we as people interpret as a smiling face with the corners of the mouth turned up is actually an appeasement sign from a nervous or submissive dog. But dogs are great people watchers and some learn to 'smile' like people, especially if given positive attention for doing it. Sadly most people can't read a dog half as well as a dog can read a human.
But a proper happy dog smile that would mean what a smile does to a human (that you're happy, friendly and relaxed) is usually done with the ears relaxed and slightly pulled down/back, eyes with a gentle expression, mouth open, tongue lolling and relaxed body language. They laugh too - very similar to the above but with a distinct heavy panting noise. My TM does that usually when he's taken the pee out of me over something or if we're out on a walk and he gets to go the way he wants to after me telling him no numerous times. :lol:
I think Sabre might be laughing at you in that photo. :lol: