In addition to @bvdputte’s solution, you probably only want to show a gallery if the page has images:
<?php if ($page->hasImages()) : ?>
<div class="pic">
<?php foreach($page->images() as $image): ?>
<figure>
<div class="box">
<img src="<?= $image->url() ?>" alt="missing image">
</div>
<div class="inline">
<span class="pic-tit">
<?= $image->Title() ?>
</span>
<span class="pic-siz">
<?= $image->WxH() ?>
</span>
</div>
</figure>
<?php endforeach ?>
</div>
<?php endif ?>
Consider using a figcaption element instead of the div inside your figure for semantic HTML: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/figure. You probably don’t need the div wrapper around your image.