function preloadImages() {
	var artbyculture = new Image
		artbyculture.src = "images/art-by-culture-on.gif"
	var artbytheme = new Image
		artbytheme.src = "images/art-by-theme-on.gif"
	var comparecontrast = new Image
		comparecontrast.src = "images/compare-contrast-on.gif"
	var viewallart = new Image
		viewallart.src = "images/view-all-art-on.gif"
}

window.onload = preloadImages;

function changeImages(sName,sImage) {
  document.images[sName].src = sImage
}