Is there a way to have a Codeigniter controller return an image?

This is not intended as One-upmanship, but pǝlɐɥʞ's suggestion is a pure PHP implementation that is not all that re-usable. You wanted to use the syntax $this->load->image('images/gorilla.png') so here is how you can.

Create /application/libraries/MY_Loader.php

<?php  if ( ! defined('BASEPATH')) exit('No direct script access allowed');

/**
 * Loader Class
 *
 * Loads views and files
 *
 * @package     CodeIgniter
 * @subpackage  Libraries
 * @author      Phil Sturgeon
 * @category    Loader
 * @link        http://codeigniter.com/user_guide/libraries/loader.html
 */
class MY_Loader extends CI_Loader {

    function image($file_path, $mime_type_or_return = 'image/png')
    {
        $this->helper('file');

        $image_content = read_file($file_path);

        // Image was not found
        if($image_content === FALSE)
        {
            show_error('Image "'.$file_path.'" could not be found.');
            return FALSE;
        }

        // Return the image or output it?
        if($mime_type_or_return === TRUE)
        {
            return $image_content;
        }

        header('Content-Length: '.strlen($image_content)); // sends filesize header
        header('Content-Type: '.$mime_type_or_return); // send mime-type header
        header('Content-Disposition: inline; filename="'.basename($file_path).'";'); // sends filename header
        exit($image_content); // reads and outputs the file onto the output buffer
    }

There are a few ways you can use this:

Basic output (default is jpeg)

$this->load->image('/path/to/images/gorilla.png');

Send mime-type to use other image types

$this->load->image('/path/to/images/gorilla.jpg', 'image/jpeg');

Return the image

$image = $this->load->image('/path/to/images/gorilla.php', TRUE);

Just like