Mdkart

This plugin for WordPress automatically add the rel=”lightbox[ID-OF-THE-POST]” to images linked in a post 
ID-OF-THE-POST is unique per post so all images per post are grouped in one lightbox set. 
Works also with the gallery Fonction of WP 2.7 and in comments
Doesn’t add the the files required for Lightbox (it only add the rel lightbox tag)! You have to insert yourself in your theme the required files or use a plugin like Lightbox 2 WordPress Plugin or Lightbox 2.3 plugin for WordPress
<h3>Changelog / Todo</h3>
0.4.1 
* Optimizing the code 
0.4 
* Now Compatible with the Gallery Fonction of WP 2.7 
* Adds also rel tag in the comments 
0.3 
* Correction of a bug that added rel tag on links done on img tags. 
0.2 
* Correction of a small bug described by Kristof Mattei. Thanks to him for the help!
Thanks to all who sent bug reports and ideas for improvements. 
Please send me a mail if I forgot you to mention here.

Add Lightbox

This plugin for Wordpress automatically add the rel="lightbox[ID-OF-THE-POST]" to images linked in a post

Benjamin Intal

This plugin behaves similarly to <a href="https://wordpress.org/plugins/regenerate-thumbnails/" rel="ugc">Regenerate Thumbnails</a> except that images are resized automatically / on the fly, when they are used. Once created, they won’t be processed again.
Your thumbnails will now resize when:
<ul>
<li>Image Sizes in Settings > Media is modified,</li>
<li>Switching themes & plugins with different thumbnail / featured image sizes</li>
</ul>
No settings pages, just install and activate and things should work right away.
Report bugs and help out in the code from the <a href="https://github.com/gambitph/WP-OTF-Regenerate-Thumbnails" rel="nofollow ugc">Github repository</a>
<h4>What are you talking about?</h4>
Test it out. In your normal WordPress website set up, create a gallery using the Add Media button while editing a post or page and use thumbnails. Afterwards, check out your gallery.
Notice the size of your thumbnails, most likely they’re 150 x 150. Do you see it? Great.
Now head over to Settings > Media and change your thumbnail size to something cooler, something rectangular, let’s try 400 x 200. Save it.
Go back to your gallery that you previously created and refresh your browser. Most likely you won’t be seeing 400 x 200 thumbnails there.
OTF Regenerate Thumbnails fixes this for you.
<h4>Usage</h4>
OTF Regenerate Thumbnails should work right away, and your images should get resized when the dimensions get changed.
For developers & tinkerers, ensuring your images get resized properly requires you to use WordPress’ image functions to display featured images and image attachments. Don’t worry, this is a good thing.
Make sure you use these WordPress functions every time you display images:
<ul>
<li><a href="https://codex.wordpress.org/Function_Reference/wp_get_attachment_image_src" rel="nofollow ugc"><code>wp_get_attachment_image_src</code></a></li>
<li><a href="https://codex.wordpress.org/Function_Reference/wp_get_attachment_image" rel="nofollow ugc"><code>wp_get_attachment_image</code></a></li>
<li><a href="https://codex.wordpress.org/Function_Reference/the_post_thumbnail" rel="nofollow ugc"><code>the_post_thumbnail</code></a></li>
<li><a href="https://codex.wordpress.org/Function_Reference/get_the_post_thumbnail" rel="nofollow ugc"><code>get_the_post_thumbnail</code></a></li>
</ul>
You can also add size names using <a href="https://codex.wordpress.org/Function_Reference/add_image_size" rel="nofollow ugc"><code>add_image_size</code></a>
<h4>Features</h4>
<ul>
<li>Creates Resizes thumbnails on the fly</li>
<li>Handles Image Size settings changes in Settings > Media</li>
<li>Handles thumbnail / image size changes introduced by switching themes & plugins</li>
<li>Works automatically, no setup needed</li>
<li>All calls to <code>the_post_thumbnail</code> and other thumbnail functions are handled automatically</li>
<li>Handles image sizes created from <code>add_image_size</code>,</li>
<li>Handles <a href="https://codex.wordpress.org/Function_Reference/the_post_thumbnail" rel="nofollow ugc">2-item array sizes</a></li>
</ul>

OTF Regenerate Thumbnails

Front end - must have

Nice plugin, very useful.
Also works on a network install.
Thanks!



Very useful

Automatically regenerates your thumbnails on the fly when thumbnail sizes change.

Add Lightbox vs OTF Regenerate Thumbnails