The frame has a full length rebate thru centre meaning only the lead edge needs a small rebate for hinge .
looking at the image on my laptop, I cannot see any rebate. Initially, I too thought there was a rebate because of the bit of timber sticking out just before the hinge knuckle, but I suspect that is just a raised bit of timber that has split away from the frame. If you look above the hinge, there is no evidence of a rebate.