images = new Array(5);

images[0] = "<a href = 'http://www.graphicsoptimization.com/gallery/im11.htm'><img src='http://www.graphicsoptimization.com/im/th/th11.jpg' alt=''></a>";
images[1] = "<a href = 'http://www.graphicsoptimization.com/gallery/im12.htm'><img src='http://www.graphicsoptimization.com/im/th/th12.png' alt=''></a>";
images[2] = "<a href = 'http://www.graphicsoptimization.com/gallery/im13.htm'><img src='http://www.graphicsoptimization.com/im/th/th13.png' alt=''></a>";
images[3] = "<a href = 'http://www.graphicsoptimization.com/gallery/im14.htm'><img src='http://www.graphicsoptimization.com/im/th/th14.png' alt=''></a>";
images[4] = "<a href = 'http://www.graphicsoptimization.com/gallery/im15.htm'><img src='http://www.graphicsoptimization.com/im/th/th15.png' alt=''></a>";

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

document.write(images[index]);