var pic1 = "images/pic1.gif";
var pic2 = "images/pic2.gif";
var pic3 = "images/pic3.gif";
var pic4 = "images/pic4.gif";
var PicNumber=1;
var NumberOfPictures=4;
var HowLongBetweenPic=3;

function SwitchPic(counter){
if(counter < HowLongBetweenPic){
counter++;
document.roll.src = eval("pic" + PicNumber);
CallSwitchPic=window.setTimeout("SwitchPic("+counter+")",1500); 		
}
else{
if(PicNumber < NumberOfPictures){
PicNumber++;
SwitchPic(0);
}
else{
PicNumber=1;
SwitchPic(0);
}
}
}