var imgRandom = new Array()
var urlImg = "<img src=\"http://www.casale-san-martino.com/images/cod/"
//var urlImg = "<img src=\"http://localhost:81/images/cod/"
imgRandom[0] = urlImg + "a.gif\" align=\"absmiddle\" />"
imgRandom[1] = urlImg + "b.gif\" align=\"absmiddle\" />"
imgRandom[2] = urlImg + "c.gif\" align=\"absmiddle\" />"
imgRandom[3] = urlImg + "d.gif\" align=\"absmiddle\" />"
imgRandom[4] = urlImg + "e.gif\" align=\"absmiddle\" />"
var mostraImg = Math.floor(Math.random() * (imgRandom.length))

document.write(imgRandom[mostraImg]);