amazon s3 path in opencart for images in config php

I am using s3 fr storing images for store in amazon web services.so i m giving the path of the s3 bucket in admin/config.php file for directory_image. The path i m giving is http://ift.tt/1L5vkrA(bucket url).

but when i m giving this path in config php file for image directory.It doesnt wrk.Please let me know if anything else also needs to be done to make the s3 path work in opencart.

Is there any extension needs to be installed to make s3 image bucket path work in opencart framework.