[TeMPOraL]

Sometimes you don't even have a photo, but rather a synthesized image that looks as if a lens was in use.

Sometimes, you want to have a system that's able to self-correct after you slap a random lens on it as it's working. Or, you're looking through a translucent material, which acts as an ad-hoc lens with unknown parameters, and you want to compensate on the go.

Point being, methods of on-line calibration without use of special calibration setup (like ArUco boards mentioned elsewhere) have a wide range of use cases and are always welcome.