This will do it. Just change both instances of "image.png" to whatever your image name will be.
First I set up a function that uses the DOM to specify the image. (The image would change onscreen if it were a different filename in the JS function.)
Then, in the body of the document, I set up a counter that calls the function every 180000 milliseconds, or every 2 minutes.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title>Test</title>
<script type="text/javascript">
function imgRefresh()
{ document.getElementById("changeMe").src = "image.png"; }
</script>
</head>
<body>
<img src="image.png" id="changeMe" />
<script type="text/javascript">
setInterval('imgRefresh()', 180000);
</script>
</body>
</html>