The players dress up in uniform, some of them with bats and gloves as props, and they take the pictures that will define them for the rest of their careers.
OK, let's not be too melodramatic here. Photo Day is one of those spring training traditions, and players from the farthest fringes of the roster get their time to shine too. Daniel McCutchen will probably never pitch for the Orioles (I said this last year about Miguel Gonzalez and look where that got me) but he gets a photograph just like everyone else.
Many, if not most, of these pictures are unremarkable. There are players, they are in uniform, wearing a hat, they are holding a bat, they are smiling, or not smiling. Yawn.
Then there's Darren O'Day. See for yourself.