Image size on random image script

Hey, im trying to change the size on the images in my code, tho i cant seem to get it work

Any ideas what i shoud add ?

<script type="text/javascript"><!--
var img = new Array();

// random images (byts varje gång sidan uppdateras)
img.push("/bikers18.jpg");
img.push("/bikers18.jpg");
img.push("/bikers18.jpg");
img.push("/bikers18.jpg");
img.push("/images/bikers18.jpg");

// How many random pictures you want to display
var num = 1;

// The part where the images are randomed and printed to screen
for(i=0;i<num;i++) {
	rand = Math.floor(Math.random()*img.length);
	document.write("<img src=\"" + img[rand] + "\" />");
}
//--></script>

Code (markup):

 

Just set the width and height