var mess = new Array
('<img src="img/runner1.jpg" alt="SYO runner" width="170" height="200">',
 '<img src="img/runner2.jpg" alt="SYO runner" width="170" height="200">',
 '<img src="img/runner3.jpg" alt="SYO runner" width="170" height="200">',
 '<img src="img/runner4.jpg" alt="SYO runner" width="170" height="200">',
 '<img src="img/runner5.jpg" alt="SYO runner" width="170" height="200">',
 '<img src="img/runner6.jpg" alt="SYO runner" width="170" height="200">'
);
var max = mess.length;
var num = Math.floor((Math.random() * max));
document.writeln(mess[num]);