<style>
input[type="image"]
{
	width: 100;
	height: 100;
	background: url(image1.png);
}
input[type="image"]:hover
{
	width: 100;
	height: 100;
	background: url(image2.png);
}
</style>
<form method="GET">
<input type="image">
</form>