What business specifically do you think this would appeal to the most?

Initially, I'd say low cost, high volume businesses with repeat daily customers. Convenience stores, coffee shops, bars, news stands. Anywhere that you could get a lot of traffic and would just need to convert a low percentage of customers.

Later, if the idea actually got traction, I can imagine that luxury businesses might want to give out high-power rewards, say a $500 upvote for a selfie with your new Ferrari, for example.