<!DOCTYPE html>
<html>
<style>
body {position: relative}
#seno {position: absolute;left:50px;top:30px}
</style>
<body>
<img id="seno" src="http://adasek.cz/menu/fotky.jpg">
 
</body>
<script>
var x = 0
var y = 0
 
function vykresli(){
 
document.getElementById("seno").style.top = y +"px"
 
document.getElementById("seno").style.left = x +"px"
 
x++
if(x>300){x=0}
}
 
setInterval(vykresli, 50)
</script>
</html>