Hi.
My target : Detect weather helmet is mounted or not
My idea is adding a camera to detect eyes. The camera is fixed outside the helmet.
Need some reference and libraries.
Thanks. 
Fitting a camera on an Arduino is not really on, let alone doing image processing.
Use an ultrasonic sensor in the hat to see if it is in a head.
We need more information on your plan. One line is totally insufficient.
Weedpharma
Ultrasonic sensor will be better but aim of this project is to detect accident and inform the location to 911 or ambulance. Making fake calls to 911 is offense. So useing camera would detect the person accurately. Using imageprocessing. So there will be no fake calls when you put your helmet down ufortunately.
And, Camera would be added to arduino yun or even uno.
Dasaradh:
And, Camera would be added to arduino yun or even uno.
I think you have severely overestimated the capabilities of the UNO.
Is this proposed safety device intended to fit inside the helmet, outside the helmet or mounted on the bike?
At the bottom of each Atmel data sheet it says:-
Unless specifically provided otherwise, Atmel products are not suitable for, and shall not be used in, automotive applications. Atmel’s products are not intended, authorized, or warranted for use as components in applications intended to support or sustain life.
I think your device falls into that category as well as being far too ambitious in scope.