It will be print as a bar code on the aadhar card so that person can be identify that , the person who is holding the aadhar card is the exact that person or not.
Just because we can change the photo which is stamp on the aadhar card but the retina code and finger print is always different to the person by person.
Finger print is taken or all the fingers of the hand by biometric finger print a
nd as the same for retina scanner we use bio enable iris scanner. Their is not any side effects of these tools if we go for these one.