var mess = new Array(

'<img src="http://www.funny-jokes-and-pictures.com/images/Funny-Joke-Giraffe-Licks-Squirrel-Best-Photo-Image.jpg" class="left" />',

'<img src="http://www.funny-jokes-and-pictures.com/images/Funny-Joke-Giraffe-Zebra-Best-Photo-Image.jpg" class="left" />',

'<img src="http://www.funny-jokes-and-pictures.com/images/Funny-Joke-Mad-Dog-Red-Eye-Best-Photo-Image.jpg" class="left" />',

'<img src="http://www.funny-jokes-and-pictures.com/images/Funny-Joke-Skate-Boarding-Elephant-Best-Photo-Image.jpg" class="left" />',

'<img src="http://www.funny-jokes-and-pictures.com/images/Funny-Joke-Weird-Mad-Cat-Best-Photo-Image.jpg" class="left" />'

);

var max = mess.length;
var num = Math.floor((Math.random() * max));
document.writeln(mess[num]);