images = new Array(5);

images[0] = "<a href = 'http://www.graphicsoptimization.com/gallery/im6.htm'><img src='http://www.graphicsoptimization.com/im/th/th6.jpg' alt=''></a>";
images[1] = "<a href = 'http://www.graphicsoptimization.com/gallery/im7.htm'><img src='http://www.graphicsoptimization.com/im/th/th7.jpg' alt=''></a>";
images[2] = "<a href = 'http://www.graphicsoptimization.com/gallery/im8.htm'><img src='http://www.graphicsoptimization.com/im/th/th8.jpg' alt=''></a>";
images[3] = "<a href = 'http://www.graphicsoptimization.com/gallery/im9.htm'><img src='http://www.graphicsoptimization.com/im/th/th9.jpg' alt=''></a>";
images[4] = "<a href = 'http://www.graphicsoptimization.com/gallery/im10.htm'><img src='http://www.graphicsoptimization.com/im/th/th10.png' alt=''></a>";

index = Math.floor(Math.random() * images.length);

document.write(images[index]);