We'll create fresh WordPress site with AOC Multiple Post Images installed. You have 20 minutes to test the plugin after that site we'll be deleted.
This plugin aims at providing users the capability to upload multiple thumbnails/featured images to a post. It uses wp.media js object to open a image uploader frame and choose/upload images. Once the images are selected, it will save the id of uploaded media object in a custom field.
You can use the function aoc_get_images($post_id) to retrieve an array of urls of all the images that have been uploaded to a post. This function accepts the id of post (for which the images are to be fetched) as a parameter.