PImage img;

void setup() {
  size(375, 500);
  background(255);
  noStroke();
  smooth();

  img = loadImage("daisies.jpg");
}

void draw() {
  for (int i = 0; i < 200; i++) {
    drawPoint(img.pixels);
  }
}

void drawPoint(int[] pixelArray) {
  int x = int(random(img.width));
  int y = int(random(img.height));
  color col = pixelArray[y * img.width + x];
  fill(col, 127);
  float pSize = 2.0 + (mouseX / (float) width) * 16.0; 
  ellipse(x, y, pSize, pSize);
}

void mousePressed() {
  background(255);
}