var imagenumber = 23;

var randomnumber = Math.random() ;

var rand1 = Math.round( (imagenumber-1) * randomnumber) + 1 ;

images = new Array
images[1] = "library/1.jpg"
images[2] = "library/2.jpg"
images[3] = "library/3.jpg"
images[4] = "library/4.jpg"
images[5] = "library/5.jpg"
images[6] = "library/6.jpg"
images[7] = "library/7.jpg"
images[8] = "library/8.jpg"
images[9] = "library/9.jpg"
images[10] = "library/10.jpg"
images[11] = "library/11.jpg"
images[12] = "library/12.jpg"
images[13] = "library/13.jpg"
images[14] = "library/14.jpg"
images[15] = "library/15.jpg"
images[16] = "library/16.jpg"
images[17] = "library/17.jpg"
images[18] = "library/18.jpg"
images[19] = "library/20.jpg"
images[20] = "library/21.jpg"
images[21] = "library/22.jpg"
images[22] = "library/23.jpg"
images[23] = "library/24.jpg"



var image = images[rand1]



document.write('<img src="' + image + '"  border="0">');