Hello ! I try to mask a live video. I want to have a image in front and the live capture in the background. I made a code but nothing happens.

The code :
import processing.video.*;
Capture myCapture;
PImage img;
PImage maskImg;

void setup(){
    size(720, 576);
    myCapture = new Capture(this, 720, 576, 30);
    maskImg = loadImage ("mask.jpg");
    img.mask(maskImg);
}

void captureEvent (Capture myCapture){
    myCapture.read();
}

void draw(){
    image(myCapture, 0, 0);
    image(img, 0, 0);
}


I think there's a mistake somewhere, I use the mask exemple of the processing exemples.
Can someone help me ?
Thanks !

You might use png with transparency to do the trick.