function changeImage() {
if (document.getElementById) {
document.getElementById("case").src="images/but-casestudies_f2.jpg";
}
else if (document.all) {
document.all["case"].src="images/but-casestudies_f2.jpg";
}
else if (document.layers) {
document.layers["case"].src="images/but-casestudies_f2.jpg";
}
}