gallery_media

<?php
$media_query = new WP_Query(
    array(
        'post_type' => 'attachment',
        'post_status' => 'inherit',
        'post_mime_type' =>'image',
        'posts_per_page' => 6,
        'orderby' => 'rand'
    )
);
$list = array();
foreach ($media_query->posts as $post) {
    $list[] = wp_get_attachment_url($post->ID);
}
$html .= '<div class="gallery">';

foreach($list as $image) {

	$html .= '<img src="' . $image . '"/>';

}

$html .= '</div>';
echo $html;