function toggle_visibility(id) {
var e = document.getElementById(id);
if(e.style.display == 'block')
e.style.display = 'none';
else
e.style.display = 'block';
}

<!-- This script and many more are available free online at -->
<!-- The JavaScript Source!! http://javascript.internet.com -->
//script for random photo array

<!-- Begin
// Set up the image files to be used.
var theImages = new Array() // do not change this
// To add more image files, continue with the
// pattern below, adding to the array.

theImages[0] = 'http://www.bcs.rochester.edu/newimages/random/000.jpg'
theImages[1] = 'http://www.bcs.rochester.edu/newimages/random/001.jpg'
theImages[2] = 'http://www.bcs.rochester.edu/newimages/random/002.jpg'
theImages[3] = 'http://www.bcs.rochester.edu/newimages/random/004.jpg'
theImages[4] = 'http://www.bcs.rochester.edu/newimages/random/005.jpg'
theImages[5] = 'http://www.bcs.rochester.edu/newimages/random/006.jpg'
theImages[6] = 'http://www.bcs.rochester.edu/newimages/random/007.jpg'
theImages[7] = 'http://www.bcs.rochester.edu/newimages/random/008.jpg'
theImages[8] = 'http://www.bcs.rochester.edu/newimages/random/009.jpg'
theImages[9] = 'http://www.bcs.rochester.edu/newimages/random/010.jpg'
theImages[10] = 'http://www.bcs.rochester.edu/newimages/random/011.jpg'
theImages[11] = 'http://www.bcs.rochester.edu/newimages/random/012.jpg'
theImages[12] = 'http://www.bcs.rochester.edu/newimages/random/013.jpg'
theImages[13] = 'http://www.bcs.rochester.edu/newimages/random/014.jpg'
theImages[14] = 'http://www.bcs.rochester.edu/newimages/random/016.jpg'
theImages[15] = 'http://www.bcs.rochester.edu/newimages/random/017.jpg'
// do not edit anything below this line

var j = 0
var p = theImages.length;
var preBuffer = new Array()
for (i = 0; i < p; i++){
   preBuffer[i] = new Image()
   preBuffer[i].src = theImages[i]
}
var whichImage = Math.round(Math.random()*(p-1));
function showImage(){
document.write('<img src="'+theImages[whichImage]+'">');
}

//  End -->