img = new Array()
ran = Math.floor(4 * Math.random());
img[0] = 'img_entrata/img4.jpg" width="902" height="217"';
img[1] = 'img_entrata/img2.jpg" width="902" height="289"';
img[2] = 'img_entrata/img1.jpg" width="902" height="238"';
img[3] = 'img_entrata/img3.jpg" width="902" height="237"';

document.write("<img src=\""+img[ran]+"\">");