import processing.video.*;

Capture cam;

int cam_width  = 320;
int cam_height = 240; 

PImage still;

void setup() {
  size(640, 480);

  cam = new Capture(this, cam_width, cam_height);
  still = createImage(cam_width, cam_height, ARGB);
}

void draw() {
  if (cam.available() == true) {
    cam.read();
    image(cam, 0, 0, width, height);
    image(still, width/2 - cam_width/2, height/2 - cam_height);
  }
} 

void keyReleased()
{
  if(key == ' ') still.copy(cam, 0, 0, cam.width, cam.height, 0, 0, still.width, still.height);
}