If you want to include a Facebook Like Button on your page, then, ordinarily, you would need to either make room for the button on your page (alongside the gallery) or overlay the container which contains the button on top of the gallery using CSS.
Details of the code to include on your web page can be obtained from this Facebook page.
For example, if you selected the HTML 5 implementation and wanted the Like Button to overlap the top-left corner of your gallery, then your web page's code would look something like this:
<!DOCTYPE html>
<html lang="en">
<head>
<title></title>
<meta charset="utf-8" />
<meta name="viewport" id="jb-viewport" content="minimal-ui" />
<meta name="description" content="" />
<style type="text/css">
body {
margin: 0px;
}
#overlay {
position: absolute;
top: 10px;
left: 10px;
z-index: 9999;
}
</style>
</head>
<body>
<div id="fb-root"></div>
<script>(function(d, s, id) {
var js, fjs = d.getElementsByTagName(s)[0];
if (d.getElementById(id)) return;
js = d.createElement(s); js.id = id;
js.src = "//connect.facebook.net/en_GB/sdk.js#xfbml=1&version=v2.0";
fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));</script>
<script src="jbcore/juicebox.js"></script>
<script>
new juicebox({
containerId: 'juicebox-container',
galleryWidth: '100%',
galleryHeight: '100%',
backgroundColor: '#222222',
galleryTitlePosition: 'NONE'
});
</script>
<div id="juicebox-container"></div>
<div id="overlay">
<div class="fb-like" data-href="https://developers.facebook.com/docs/plugins/" data-layout="standard" data-action="like" data-show-faces="true" data-share="true"></div>
</div>
</body>
</html>
Perhaps an easier method would be to select the IFRAME implementation of the Like Button and paste the entire iframe code into the Gallery Title text field in JuiceboxBuilder-Pro (in the 'Customize -> Lite' section). If trying this, I would also recommend setting galleryTitlePosition="TOP" (in the 'Customize -> General' section) so that the Like button is always visible in your gallery.
Please note that the Like Button will not be displayed until you upload your gallery to your web server.
I hope this helps.