Fingerprint Scanner getFingerprintIDEz()

Under this code is to check if you're fingerprint is registered in scanner.
But there's no way to tell you if its not in registered in scanner.

int getFingerprintIDez() {
  uint8_t p = finger.getImage();
  if (p != FINGERPRINT_OK)  return -1;

  p = finger.image2Tz();
  if (p != FINGERPRINT_OK)  return -1;

  p = finger.fingerFastSearch();
  if (p != FINGERPRINT_OK)  return -1;
  
  // found a match! 
  
  Serial.print("Found ID #"); Serial.print(finger.fingerID); 
  Serial.print(" with confidence of "); Serial.println(finger.confidence);
  BTSerial.println(finger.fingerID);
  Serial.print(finger.fingerID);   
  return finger.fingerID; 
}

It always return -1 when no finger has scan.
delay(); won't work because what if user takes longer to input his finger to the scanner.
Is it possible to tell if the finger scanned is not registered in scanner?

You could have each error return give you a different (negative) error number. Then your program could distinguish between bad image, bad transform and print not found. That last case is as close as you can get to finger not registered, although of course it may be that it is registered but the scanner failed to recognize it.