The traditional way to see marks on the back of mahjong, Domino and Paigow is to wear a pair of IR contact lenses or IR sunglasses. But this is different from the leather belt camera.
We have marked mahjong, Domino and Pai gow with a special ink and these marks only can be read by the belt camera. You could see them clearly on a TV or a Phone in the background. And then you could know what these marks are from your partners. We need to mention the distance from the belt camera lens and the mahjong tiles. The short scanning distance is 20-40cm. and the long scanning distance is 1.5 meters.