1. http://www.fbi.gov/about-us/cjis/fingerprints_biometrics/recording-legible-fingerprints/
2. http://inklessfingerprinting.com/inkless-thumbprint-pads/catalog/index.php
3. http://www.inklessprints.com/inklesssystems.html
4. http://www.alternateforce.net/dig10infin.html