This is a really simple and a bit stupid image lightbox jQuery plugin. It has no options and works out of the box. It just a javascript jquery.stupidbox.js file with no styleshets, images, etc. And just the "X" letter is used as a closing icon.

And again, all you need is jquery.stupidbox.js (it's around 30 lines of code).

Demo on CodePen

The idea of this markup is that <a> tag has a big image and <img> has a thumbnail.

<a href="big-image.jpg">
    <img src="thumbnail-image.jpg">
</a>

Or you can use just <img> tag. In this case, you will get the same image in the lightbox.

<img src="image.jpg">

jQuery(function ($) {
    $("a").stupidbox();
});

Or:

jQuery(function ($) {
    $("img").stupidbox();
});

We stretch image in the lightbox to full screen keeping aspect ratio, so it's recommended to use high quality images for "big image".