The boards have been planed to thickness and jointed on their edges. The photo shows the boards stacked on edge, where they are examined for accuracy in the joints. No light should show through the joints or else the joints will be weak and subject to subsequent failure. Besides, inaccurate joints look ugly. This panel has not yet been glued together!
Notice that the panel shows some camber (cupping). This is deliberate, in order to compensate from the beginning for the tendency of a relief panel to cup to the carved side. The carving pattern will be drawn onto the CONVEX side of this panel.