How can you in good conscience charge a subscription for this? It would be one thing if the app relied on infrastructure, but it's a one and done algorithm that's entirely local on device!

Subscriptions are charged because the developer needs to maintain the upkeep and cost of running the service, but that's not applicable here. It's capable of taking a million photographs fully offline, without any reliance on an online service.

Essentially you're saying your product is so superb that people should pay you indefinitely for the privilege of using it. Even though it costs you nothing to maintain, you somehow need people to perpetually pay you for a local, offline algorithm that you wrote one time. How gross, that's the definition of pointless greed.

Shame on you, honestly. This is exactly what's wrong with modern software nowadays. Just like Adobe and all these other companies, taking advantage of people to milk them dry forever. You'll lease a product, you won't have the right to own anything, and you'll be happy about it.