I have been working on how to reduce the jitter and till some extent I have been able to do it, but now I dont find any way on how to implement it to multiple faces.

this works as charm for single face.....

image(otherFaceImage,lastX,lastY, lastWidth, lastHeight);                     
         lastWidth = lastWidth +  ((faces[i].width - lastWidth)* followSpeed / 5);
          lastHeight = lastHeight + ((faces[i].height - lastHeight)* followSpeed / 5);
          lastX = lastX + ((faces[i].x - lastX)* followSpeed / 3.5);
          lastY = lastY + ((faces[i].y - lastY)* followSpeed /3.5);


help help...