var imagenumber = 18 ;
var randomnumber = Math.random() ;
var rand1 = Math.floor( (imagenumber) * (randomnumber-.00001)) + 1 ;

pictures = new Array
pictures[1] = "images/pic1.jpg"
pictures[2] = "images/pic2.jpg"
pictures[3] = "images/pic3.jpg"
pictures[4] = "images/pic4.jpg"
pictures[5] = "images/pic5.jpg"
pictures[6] = "images/pic6.jpg"
pictures[7] = "images/pic7.jpg"
pictures[8] = "images/pic8.jpg"
pictures[9] = "images/pic9.jpg"
pictures[10] = "images/pic10.jpg"
pictures[11] = "images/pic11.jpg"
pictures[12] = "images/pic12.jpg"
pictures[13] = "images/pic13.jpg"
pictures[14] = "images/pic14.jpg"
pictures[15] = "images/pic15.jpg"
pictures[16] = "images/pic16.jpg"
pictures[17] = "images/pic17.jpg"
pictures[18] = "images/pic18.jpg"
var picture = pictures[rand1]