PImage img;

int imgScale = 8;

int pointillize = 10;

void setup ()  {
  size(500, 500);
  img = loadImage("Roofing.jpg");
  background(255);
  smooth();
}

void draw()  {
  int x = int(random(img.width));
  int y = int(random(img.height));
  int loc = x + y*img.width;
  
  loadPixels();
  float r = red(img.pixels[loc]);
  float g = green(img.pixels[loc]);
  float b = blue(img.pixels[loc]);
  fill(0);
  strokeWeight(1);
  fill(r,g,b,100);
  ellipse(x,y,pointillize,pointillize);
}