function pickImageFrom(whichGallery)
{

var gallery = new Array();
gallery[0] = new Array("1a.jpg","1b.jpg","1c.jpg","1d.jpg");
gallery[1] = new Array("2a.jpg","2b.jpg","2c.jpg");

var idx = Math.floor(Math.random() * gallery[whichGallery].length);
document.write('<img src="images/random/' + gallery[whichGallery][idx] + '">');
}