After 10 years of development, including a 2 1/2 year delay, the US has finally introduced the new $100 banknote into the circulation. This banknote employs two new security features: a three-dimensional blue strip with images that appear to move when the note is tilted, and an image of a copper inkwell containing a holographic bell whose colour changes when tilted. These features, along with the more traditional security, are designed to ensure that accurate reproduction of the note will be very difficult. Along with the fact that the $100 bill is the most counterfeited bill in US currency, the Federal Reserve estimates that 1/2 – 2/3 of $100 bills in circulation are outside of the United States. The new security features will be extremely important in reducing the number of illicit bills in the international market
Further information:
http://www.bbc.co.uk/news/technology-24431952
http://business.financialpost.com/2013/10/07/new-us-100-bill/.