See if you can follow a grain line from one end to the other. It might be difficult because that board appears to be perfectly flatsawn, so the flat faces will be pretty boring looking and difficult to track. If you can see anything running along the length at the edges, it might help. In the event that the billet isn't running dead straight where the rift grain surfaces, then you'll want to follow the lines (which means you might get two billets instead of three), especially if they're parallel to each other but not to the side of the billet (if that makes sense).

You're far better off with two well behaved billets than three duds.

It occurs to me as I'm typing this that a fairly reliable way of checking is to see if the grain orientation looks identical on both ends. If it does, it's probably in good orientation to be sawn.