var state = 0;
var originalImage;

function rotate(imageElement, image1URL, image2URL) {
  if (state==0) {
    state=1;
    originalImage = imageElement.src;
    imageElement.src = image1URL;
    }
  else if (state==1) {
    state=2;
    imageElement.src = image2URL;
    }
  else if (state==2){
    state=0;
    imageElement.src = originalImage;
    }
  }