Bjørn Johansen

This is a WordPressified version of the excellent, lightweight (for real!) imageLightbox.js (MIT-licensed) by Osvaldas Valutis (http://osvaldas.info/image-lightbox-responsive-touch-friendly)
This is his introduction to the lightbox: 
“As for the image lightboxes, I have always lacked simplicity for them. I mean not only the visual design, but the overall experience: from implementation to UX. All due respect, but I have never liked any of these light-fancy-face-boxes. They all were solving problems that just don’t exist: lots of unwanted features by default, total mess in markup, no native behavior for touch screens. I was working on a project and needed an image lightbox that solves these problems. I needed a lightbox only for images, not video, text, and iframes at once. I made ImageLightbox.js.”
This version autodetects all links to image files and opens them in the lightbox.
For your “install, activate and go”-convenience, this plugin comes with a minimal CSS that easily can be deactivated and/or replaced.
The plugin can also be themed to your liking. An example theme is available here: https://github.com/bjornjohansen/imagelightbox-theme-smooth
Please let me know if you have any issues. Fastest way to get a response is by Twitter: https://twitter.com/bjornjohansen

imageLightbox

Image Lightbox, Responsive and Touch‑friendly.

WeDOK

WePOP is a lightweight, jQuery-free image popup plugin for WordPress. 
It is designed for long-term stability, simplicity, and compatibility — even as WordPress or jQuery evolves. 
Built entirely with pure JavaScript, it works across all modern themes and requires no shortcodes or external libraries. 
Now supports mobile swipe gestures for navigating popup images.
Unlike complex popup plugins with unnecessary features, WePOP was developed by a seasoned creator at WeDOK, a web studio with years of real-world client work. 
WePOP focuses on just the essential features needed for modern websites — fast, clean image popups with easy configuration.
<h3>⚙️ Show Alt Text</h3>
Display the image’s alt attribute below the popup image as a caption. 
This improves accessibility and allows for simple descriptions without needing custom fields or captions.
<h3>⚙️ Popup Mode</h3>
You can choose how image links are grouped into popup viewers using the Popup Mode setting:
<ul>
<li>
Gallery Blocks Grouping Mode 
Only images inside WordPress Gallery blocks are grouped into popup slideshows. 
If your post includes multiple Gallery blocks, each one will be treated as a separate group. 
Other images open individually without navigation.
</li>
<li>
All Images Grouping Mode 
All image links in the post are grouped into a single popup viewer with navigation arrows, 
regardless of whether they are in gallery blocks or standalone.
</li>
<li>
No Grouping Mode 
All images open in their own individual popup windows with no grouping or navigation arrows.
</li>
</ul>
<h3>⚙️ Language</h3>
WePOP supports a multilingual interface. You can select your preferred admin language from the plugin settings.
<ul>
<li>🇯🇵 Japanese (ja_JP) </li>
<li>🇺🇸 English (en) </li>
<li>🇪🇸 Spanish (es) </li>
<li>🇫🇷 French (fr) </li>
<li>🇩🇪 German (de) </li>
<li>🇨🇳 Simplified Chinese (zh_CN) </li>
<li>🇮🇹 Italian </li>
<li>🇰🇷 Korean </li>
<li>🇧🇷 Portuguese (Brazil)</li>
</ul>
WePOP is ideal for developers, bloggers, and creators who need a fast and reliable image popup tool — 
without the bloat or complexity of traditional lightbox plugins.

WePOP

WePOP is a lightweight image popup plugin for WordPress that works without jQuery or external libraries.

imageLightbox vs WePOP