WordPress plugin for loading images from production on a staging/development website. See https://hookturn.io/load-media-images-from-production-wordpress-plugin/

load-images-from-production.php

<?php
/**
 * Plugin Name: Load Images From Production (for staging/dev)
 * Description: Hooks into WP's media URL generation and replaces the domain with the production domain.
 * Author:      Phil Kurth
 * Author URI:  https://hookturn.io
 */

// If this file is called directly, abort.
defined( 'WPINC' ) or die();

// Configure these
defined( 'LIFP_PRODUCTION_HOST' ) or define( 'LIFP_PRODUCTION_HOST', '' );
defined( 'LIFP_PRODUCTION_SCHEME' ) or define( 'LIFP_PRODUCTION_SCHEME', 'https' );

// If prod host name hasn't been defined, bail.
if ( empty( LIFP_PRODUCTION_HOST ) ) {
	return;
}

add_filter( 'wp_get_attachment_image_src', function ( $image, $attachment_id, $size, $icon ) {
	$parts = parse_url( $image[0] );

	// Override with prod values.
	$parts['scheme'] = LIFP_PRODUCTION_SCHEME;
	$parts['host'] = LIFP_PRODUCTION_HOST;

	// Ensure all keys are set.
	$parts = array_merge( [ 'path' => '', 'query' => '' ], $parts );

	// Build the new URL.
	$image[0] = "{$parts['scheme']}://{$parts['host']}{$parts['path']}";
	if ( $parts['query'] ) {
		$image[0] .= '?' . $parts['query'];
	}

	return $image;
}, 10, 4 );

wp-config.php

<?php

// Configure these in your wp-config.php file...

define( 'LIFP_PRODUCTION_HOST', 'www.mycoolsite.com' );
define( 'LIFP_PRODUCTION_SCHEME', 'https' ); // Optional.