test

<div class="gallery">
    <?php
    $images = get_posts(array(
        'post_type' => 'attachment',
        'post_mime_type' => 'image',
        'posts_per_page' => -1,
        'post_status' => 'any'
    ));

    foreach ($images as $image) {
        echo '<div class="gallery-item">';
        echo '<img src="' . wp_get_attachment_url($image->ID) . '" alt="' . get_post_meta($image->ID, '_wp_attachment_image_alt', true) . '" />';
        echo '<div class="caption">' . $image->post_title . '</div>';
        echo '</div>';
    }
    ?>
</div>

<div id="myModal" class="modal">
    <span class="close">&times;</span>
    <img class="modal-content" id="img01">
    <div id="caption"></div>
</div>