Perhaps the gamification portion of the app can be linked to actual products i.e prizes that the app user can redeem for in shops after achieving a certain badge. If logistics is an issue (presumably the app will be rolled out worldwide and it might be hard to get buy-in from retailers), the app sponsoring company can also consider having a "Hall of fame" on their official website to show the scorings made by contributors in each country to inspire positive competition to encourage greater recycling. This "Hall of fame" could be linked to Facebook, Twitter etc to gain more publicity and exposure on recycling efforts by different countries. The converse is also true, as countries down on the chart might inspire the citizens/government to re-think their recycling mindset and policies in the country.
Recycling machines for bottles and cans can also be linked to the app to ensure that the barcode scanning action is actually translated into genuine recycling. I recall the existence of a drinks can recycling machine (looks similar to a vending machine) in Singapore more than a decade ago where people got vouchers for shops located in the mall if they recycled more than 20 cans at one go. There were queues forming at the recycling machine every weekend evening!