People WON'T wait around if the headshots are not of very high quality, and if there is not real-time sharing that allows the headshots to go viral within the conference.
HOWEVER, people will wait 15 to 90 minutes for a very good headshot because they know it will cost them $300 to over $1,000 to get a very good headshot back home. The sponsors who hire me realize that in a way it’s like you're handing out
$500 bills. Hence the huge lines.