Correct path for images in javascript using Cakephp -

i new in cakephp, , have script, converted cakephp. have there rotate background use 4 images this:

$.backstretch([     "img/bg/1.jpg",     "img/bg/2.jpg",     "img/bg/3.jpg",     "img/bg/4.jpg" ], {      fade: 1000,      duration: 8000 }); 

when open script name_domain.com use controller users , action login, see images , work perfect, when try use register (controller=>users, action=>signup) images not load. put ../img.... working here , not in index.

how can link correctly images. try "/img" not working.

any appreciated.

declare javascript variable in default.ctp

var image_host = "<?php echo $this->webroot.'/img/'; ?>"; 

and can use in javascript file too

<script> $.backstretch([     image_host + "bg/1.jpg",     image_host + "bg/2.jpg",     image_host + "bg/3.jpg",     image_host + "bg/4.jpg" ], {      fade: 1000,      duration: 8000 }); 

hope helps..!!