Where do I put image files, css, js, etc. in Codeigniter?

I have a setup like this:

I then have a helper function that simply returns the full path to this depending on my setup, something similar to:

application/helpers/utility_helper.php:

function asset_url(){
   return base_url().'assets/';
}

I will usually keep common routines similar to this in the same file and autoload it with codeigniter’s autoload configuration.

Note: autoload URL helper for base_url() access.

application/config/autoload.php:

$autoload['helper'] = array('url','utility');

You will then have access to asset_url() throughout your code.