Why not automate the process of iris scanning somewhat by having monitored booths or rooms. They could be monitored by cameras and a local or remote human presence that can intervene but has limited communication abilities to prevent potential for bribery?
Unless a basic income is global, immigration problems are only going to get more difficult.
Any sort of "decentralized" network of autonomous agents acting at the behest of identity verification would be extremely easy to game. There must be some incentive for these verifiers to act as an agents of the protocol, so you would assume they are compensated with SocialCoin. This is an incentive that is easy and rational to abuse.
Syndicates of agents will most likely pop up and commoditize iris scans or whatever the verification procedure requires. They'd quickly spoil the payouts for people without massive numbers of identities under their control.
Not only are they paid to sign people up, but they also can MITM payouts from unsuspecting individuals.
Unless a basic income is global, immigration problems are only going to get more difficult.