var crossingCounter=0;
var actionCounter=0;
var blinkTriggered=0;
var actionsDone=0;
var thumbDOM;

function user_bored(){
  crossingCounter++;
  if (crossingCounter> actionCounter*3+3){
    actionCounter++;
    trigger_action();
  }
}

function trigger_action(){
  if(blinkTriggered){
    return;
  }
  blinkTriggered=1;
  setTimeout(change_thumbnail,2000);
}

function change_thumbnail(){
  thumbDOM.setAttribute("src","/~estan/pictures/th"+(actionsDone%2)+".jpg");
  setTimeout(restore_thumbnail,500);
}

function restore_thumbnail(){
  thumbDOM.setAttribute("src","/~estan/pictures/thumb.jpg");
  actionsDone++;
  if (actionCounter>actionsDone){
    setTimeout(change_thumbnail,5000);
  } else {
    blinkTriggered=0;
  }
}