Perceptual hashing - Match Pokemon cards through a lens to reference JPG images

iOS eng pro, CV n00b here. I have ambitions to create an iOS card scanner app like this one here:

https://apps.apple.com/us/app/bigar-pok%C3%A9-card-scanner/id1199495742

This app works amazingly well, mine is just OK. Right now my approach is

1. Detect the shape of the card, then extract the image buffer
2. Perform a perspective transform to get the "rectangle" shape
3. Generate 3 separate pHash values for R, G, B channels
4. Lookup against a database of precomputed pHash values of card images …

computervision hashing images pokemon reference