var pic_a="images/pic_1.jpg";
var pic_b=" images/pic_2.jpg";
var pic_c="images/pic_3.jpg";
var pic_d="images/pic_4.jpg";
var pic_e="images/pic_5.jpg";
var pic_f=" images/pic_6.jpg";
var pic_g=" images/pic_7.jpg";
var pic_h=" images/pic_8.jpg";
var pic_i=" images/pic_9.jpg";
var pic_j=" images/pic_10.jpg";
var pic_k=" images/pic_11.jpg";
var pic_l=" images/pic_12.jpg";

function reveal(whichpic){
document.images["picture"].src=whichpic;
}