var current = 0;
var myPics = new Array();
function addPic(_p) {
  myPics[myPics.length?myPics.length:0] = new Image();
  myPics[myPics.length-1].src=_p; // preload all pics
}

addPic("images/million.jpg");
addPic("images/kid4.jpg");
addPic("images/child.jpg");

function checkIt(val) {
  current = Math.abs((current+parseInt(val))%myPics.length);
  document.myimg.src = myPics[current].src;
}