// This will swap the image from the image tag with id='swapimg'
// with the imgfile specified. the file path specifed in imgfile
// will be prepended by 'images/' and set the text into the element
// 'overlay'

function swap(imgfile, text) {
	document.getElementById('swapimg').src = 'images/' + imgfile;
	document.getElementById('overlay').innerHTML = text;
}