435,607 duplicate currency notes were detected In 2010-2011. This number is for bank branches by individual customers.
We read in news about duplicate currency notes. These notes make Indian economy dull. Once a note is identified as duplicate it is no more in transaction. I have not seen a duplicate note in my life but there is a black empire of duplicate currency notes. Distributing duplicate notes is a huge lose to Indian Government.

As we know the bank of banks in India is Reserve Bank of India. Reserve bank of India has created a website to make aware of duplicate currency notes. You can visit the website here http://www.paisaboltahai.rbi.org.in/ to read the security features in an Indian rupee note. Indian government has issued 1000 rupee notes, 500 rupee notes, 100 rupee notes, 50 rupee notes, 20 rupee notes and 10 rupee notes. There are other notes as 5 rupee notes but in the market there are chances to distribute duplicate notes for 100 rupee, 500 rupee and 100 rupee. 10 rupee and above notes have some of the special security features.

10 rupee note has 7 security features. 20 rupee, 50 rupee and 100 rupee notes have 10 security features. 500 and 1000 rupee notes have 11 security features. These all security features help you to identify original notes and detect duplicate notes.

On the website numbers on the note as you can in above screenshot, when you click on the number you will see the detail of the feature.

You can go ahead here http://www.paisaboltahai.rbi.org.in/