Capture modality
Fingerprint captures are tagged with a modality: 'contactless' or 'scanner'.
The matcher (SourceAFIS, server-side) tunes its decision threshold per modality. Contactless captures have lower effective DPI and noisier ridge contrast than scanner captures, so the same raw similarity score corresponds to a different genuine-versus-impostor distribution. Without per-modality tuning, contactless verifications would either accept too many impostors or reject too many genuine subjects.
Captures driven by the camera-based FingerprintCaptureSession are always 'contactless'. The 'scanner' value is used when capturing through a USB reader via FingerprintReaderClient or when submitting pre-captured scanner-grade images through BiometricsApi directly.