Snippet for OpenCV to detect hand gestures....

drawContours( thr, contours,largest_contour_index, color, CV_FILLED, 8, hierarchy ); // Draw the largest contour using previously stored index.
 drawContours( thr, hullP, 0, color, 1, 8, vector(), 0, Point() );
 ellipse(src, minellipse[0], color, 2, 8 );
 findContours( thr, contours, hierarchy,CV_RETR_CCOMP, CV_CHAIN_APPROX_SIMPLE );