This plugin allow to build development environnement without copy data from uploads folder. Manage an failback with PHP and production assets.

prod-images.php

<?php
/*
 * Plugin Name: BEA - Prod images
 * Version: 0.1
 * Plugin URI: http://www.beapi.fr
 * Description: This plugin allow to build development environnement without copy data from uploads folder. Manage an failback with PHP and production assets.
 * Author: BeAPI
 * Author URI: http://www.beapi.fr
 * Domain Path: languages
 * Network: false
 *
 * --------------
 * Copyright 2015 - BeAPI Team (technique@beapi.fr)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 *
 * --------------
 * 
 * 		Installation usage for WPms subfolder
 * 
 * 		You need to add the following rule before this line "RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]"
 * 			RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-content/uploads.*) $1 [L]
 * 
 */

if ( !defined('UPLOADS_STRUCTURE_NAME') ) {
	define('UPLOADS_STRUCTURE_NAME', 'wp-content/uploads');
}

if ( !defined('PROD_UPLOADS_URL') ) {
	define('PROD_UPLOADS_URL', 'http://myproddomain');
}

if ( false !== strpos($_SERVER['REQUEST_URI'], UPLOADS_STRUCTURE_NAME) ) {
	// Get extension
	$extension = pathinfo( $_SERVER['REQUEST_URI'], PATHINFO_EXTENSION );

	// Send content type header
	header('Content-Type: '.get_mime_type_from_file_extension($extension));

	// Get remote HTML file
	$response = wp_remote_get( untrailingslashit(PROD_UPLOADS_URL) . $_SERVER['REQUEST_URI'] );

	// Get response code
	$response_code = wp_remote_retrieve_response_code( $response );
	
	// Check for error and the response code
	if ( !is_wp_error( $response ) && 200 == $response_code ) {
		// Parse remote HTML file
		$data = wp_remote_retrieve_body( $response );

		// Check for error
		if ( !is_wp_error( $data ) ) {
			status_header(200);
			echo $data;
			exit();
		}
	}

	header('Content-Length: 0');
	exit();
}

function get_mime_type_from_file_extension( $extension ) {
	global $phpmailer;

	// (Re)create it, if it's gone missing
	if ( ! ( $phpmailer instanceof PHPMailer ) ) {
		require_once ABSPATH . WPINC . '/class-phpmailer.php';
		require_once ABSPATH . WPINC . '/class-smtp.php';
		$phpmailer = new PHPMailer( true );
	}

	return $phpmailer->_mime_types( $extension );
}