Transparent Images

PImage pic;
int alpha = 255;
int offset = -5;

void setup()
{
   size(800,500);
   pic = loadImage("run.jpg");
}

void draw()
{
   background(255);
   tint(255, 255 - alpha);
   image(pic, 0, 0);
   tint(255,alpha);
   if (frameCount % 3 == 0)
      alpha += offset;
   image(pic, 180, 150, 200 ,200);
   if (alpha < 0)
      offset *= -1;
   if (alpha > 255)
      offset *= -1;
}