Well, I believe they are created automatically for All-Stars and World Champions if you have the option set in Game Setup, Player and Picture Options.
If the option is on, then you can click a button on the player profile as well, under Pictures. A dialog comes up in which you can name the card and select from a number of formats included with the game.
I also know that it's very easy to load one saved game after another, so you can switch back and forth. I'll let somebody else comment on the photos; I play strictly fictional but I am aware of historical photos and FaceGen images of real players that can be loaded into the game. If nobody answers, try these online manual links:
Out of the Park Baseball Manual
Out of the Park Baseball Manual
Here's the pic with the baseball card menu item: