Fun fact: The treasury department won't tell you what is actually on the bills. In fact, none of the governments will. You can analyze them till you're blue in the face, under whatever light or circumstances you want, but the treasury department won't tell you what security measures are on the bill, nor when they change them. Additionally, they sometimes change during print runs, and issues.

> the treasury department won't tell you what security measures are on the bill, nor when they change them

Here are a few Treasury Department webpages telling you what security measures are on the bill, and they publish a press release with a new interactive site when they change them:

http://www.newmoney.gov/newmoney/flash/interactive100/index....

http://www.newmoney.gov/uscurrency/redesigned100.htm

http://www.moneyfactory.gov/anticounterfeiting/securityfeatu...

These are what they tell you about.

Fun fact: you are asking the wrong branch of the government.

The Secret Service will happily tell you about security features of currency, and behind closed doors help you build methods to detect counterfeits if you have a reasonable justification.

http://www.secretservice.gov/know_your_money.shtml

Fun fact: 'branch of government' refers to the executive, legislative, and judicial branches. Nearly everything is under the 'executive branch'.

</pedantry>

The secret service is under the treasury dept.

They used to be under the Treasury Dept. They are now under the Dept. of Homeland Security:

http://www.dhs.gov/department-components

TIL

No kidding!? I did not know, nor expect that.