Wordpress - Get All Images in Media Gallery?

$query_images_args = array(
    'post_type'      => 'attachment',
    'post_mime_type' => 'image',
    'post_status'    => 'inherit',
    'posts_per_page' => - 1,
);

$query_images = new WP_Query( $query_images_args );

$images = array();
foreach ( $query_images->posts as $image ) {
    $images[] = wp_get_attachment_url( $image->ID );
}

All the images url are now in $images;

$media_query = new WP_Query(
    array(
        'post_type' => 'attachment',
        'post_status' => 'inherit',
        'posts_per_page' => -1,
    )
);
$list = array();
foreach ($media_query->posts as $post) {
    $list[] = wp_get_attachment_url($post->ID);
}
// do something with $list here;

Query the db for all media library items (not just ones attached to posts), grab their url, dump them all in $list array.

<?php
    $attachments = get_children( array('post_parent' => get_the_ID(), 'post_type' => 'attachment', 'post_mime_type' =>'image') );
    foreach ( $attachments as $attachment_id => $attachment ) {
            echo wp_get_attachment_image( $attachment_id, 'medium' );
    }
?>

This pulls all attachments for a post/page. Attach more images to a post, and it will be listed