Hi -- many Android phones have USB host mode, meaning you can connect USB devices like keyboards and webcams. But none that I know of have webcam drivers. It's unclear if android browsers would recognize video devices even if they did, although that's not strictly required for Infragram, if you just upload instead of doing live conversion.
I wonder if you had a Raspberry Pi with a webcam attached, and made it stream the video over a PeerConnect connection in WebRTC -- we should be able to receive that in theory in Infragram.org. But it's a pretty big coding project to get something like that working.
Sorry there's not an easier answer! It would be super great to do.
There are some apps that connect to external webcams, but some need root access, and I tried a couple and couldn't get them to work. You could try them out for taking a webcam picture, then uploading it to Infragram.org?
Jeff