Investigate self-checkin workflow via App

Loewi:
Now that we have data matrix codes we could develop a "speed checkin" since we could place the code into the app and then make one or two queues with scanners - so that they scan their code out of the app and just present their photoid/passport

A second scan from the badge could set the status "checked in" - this way we could make sure the right badge is given out even