adamprohack

<h3>What does this plugin do?</h3>
This plugin generate image thumbnails only when site need it, when someone call function with needed size, 
and saves disk space when image is uploaded to media library. 
You don’t need to use <code>add_image_size()</code> function.
<h3>How it works?</h3>
<ol>
<li>Upload image to media library</li>
<li>Change function <code>wp_get_attachment_image_url()</code> to <code>get_otf_image_url()</code> in your wordpress template</li>
<li>When function is invoke the first time, the image is dynamically adjust, create and stored</li>
<li>Page serve image in need size</li>
</ol>
<h3>Documentation</h3>
<pre><code>`php
function get_otf_image_url(
 $image_id, $size_name, 
 $width = 0, $height = 0, 
 $crop_mode = ["center", "center"], 
 $mime_type = "image/jpeg", $quality = 70)
`
</code></pre>
Parameters
<ul>
<li>Required: 
*$image_id – attachment id 
***$size_name** – dynamic size name 
***$width** – image width 
***$height** – image height</li>
<li>Optional 
*$crop_mode – image crop mode 
***$mime_type** – result image mime type 
***$quality** – result image quality</li>
</ul>
Return Value
<ul>
<li>Returns an url string</li>
</ul>

WP Images OTF Plugin

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.

WP Images OTF Plugin vs OTF Regenerate Thumbnails