OpenCV License in a Free Android APP with purchases

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Hi! I am building an Android App Wich is Free but it have purchases. The app is for backgound change (Photos) and other things, eg: you upload a photo and change the background. the core of the app is in OpenCV with third party libraries included. The app is free to download (includes Ads) with few background photos. But if you want more backgrounds to change you need to buy the backgrounds photos.

How works the license in this case?

Thanks!