Aadhar card is a one of a kind unique scheme offered by the Government of India. Whenever a citizen of India or NRI applies for a new Aadhar card, details like his full name, DOB (date of birth), fathers name, full residential address, all finger print scans and eye retina scan are registered in the Aadhar card database.
All this information of a perason is collected and is stored in a barcode which is unique for that person. That barcode contains the Aadhar Number which is also known as UID number. It is unique that person and we can identify whether the person holding the UID card is that person or not.
People can forge the Aadhar ard photo but the finger print scans and the eye retina scans are unique for every person on this planet earth.
Finger prints of all the fingers of your hand are taken bsy a biometric fingerprint scanner and also the retina of both the eyes are scanned using a biometric iris scanner. They have common scanners at the Aadhar card enrolment center and they do not cause any side effects after using them.