var animal_imgs = new Array("/_resx/images/common/giraffe.png","/_resx/images/common/meerkat.png");
var animal_ids = Array("giraffe", "meerkat");
function writeImage()
{
    var i = (Math.round(Math.random()*(animal_imgs.length-1)));
    var src = animal_imgs[i];
    var id = animal_ids[i];
    
    document.write('<img id="'+ id +'" src="' + src + '">');
}