PImage img;
img = loadImage("sample.jpg");
size(800, 597);
imageMode(CENTER);
noStroke();
background(255);
for ( int i = 0; i < img.height; i=i+10 ) {
  for ( int j = 0; j < img.width; j=j+10 ) {
    color c = img.get(j, i);
    fill(red(c),green(c),blue(c));    
    text("A",j,i);
  }
}