Puoi fare cosi
codice:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>Untitled</title>
<script language="JavaScript" type="text/javascript">
<!--
function changeSize(id_immagine,iWidth,iLength) {
document.getElementById(id_immagine).width = iWidth;
document.getElementById(id_immagine).length = iLength;
}
//-->
</script>
</head>
<body>
[img]chartreuse0003.jpg[/img]
<input type="button" value="200 x 200" onclick="changeSize('immagine',200,200)">
<input type="button" value="300 x 300" onclick="changeSize('immagine',300,300)">
</body>
</html>