I'd love to see a way to have a person pick a card and then it end up as their wallpaper on their phone. Is that possible? It's probably breaches security. I'm not familiar with NFC enough to know. Can anyone tell me? Is there a way to send an image to a random phone and have it display as their background? Or even just display on their phone?
It's probably not possible to have the image come onto the phone as a wallpaper, the image has to be on the phone in the first instance. However if the images were on the phone it is possible for the ring to trigger a change in wallpaper. I use hdim detect in one app to trigger tasker to change another app that can change live wallpapers or normal wallpaper.
The ring itself probably cannot store enough data for a wallpaper image.
However you could use the ring to take your self to a URL that could have that image on it, but for it to happen seamlessly on a random phone could be tricky.
I would think a particular phone that was set-up right would be the best option.