how to combine sift source code with the camera ?

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Can you please provide your code and explain your problem ?

You can get help about SIFT implementation from here and here

If you want to configure camera you just need to add

CvCapture* capture;
capture = cvCaptureFromCAM( 0 );

cvCaptureFromCAM will allow you to choose different cameras . Then just take notes regarding which camera corresponds to which number.