Again, it is too easy to cheat the system. CMs are likely not looking very hard at DAS pictures, and there is really little benefit in one person in a party from holding the DAS vs another as is. If you added the "benefit" of avoiding height measurements, there would be some parents willing to risk their child's health. An under-height person on the ride exposes Disney to liability they don't want and, from their perspective, easily avoided.
I've never needed a DAS card, so really don't know what is involved. I have no idea how big or clear the pictures are. I just thought the picture would idenitfy the person and thus confirm yea or nay on height. And not speaking of every child using DAS as getting measured at GS, just those who have trouble standing. But as I said, never needed it so really don't know the ins and outs.