zlabs

Picgrab is a plugin that download, resize and crop an image on the fly. 
Simply add the “resize” attribute in the img tag you want to grab & resize on your post.
E.g. 
<img src=”http://farm4.static.flickr.com/3532/3243887563_700849f242.jpg” resize=”402×200c;66y” /> 
Once activated, the plugin replaces the attribute “src” on img tags containing the “resize” attribute with something like:
http://yoursite/wp-content/plugins/picgrab/resize.php?url=<coded characters>&size=<coded characters> 
and removes the “resize” attribute.
The resize.php script included with plugin does the work to grab, crop and resize the image. 
It also manages the cache. 
The resize attribute format is:
[(x0,y0,xs,ys)]<xd>x|x<yd>|<xd>x<yd>[c[<crop>]][;<cachetime>]
e.g. 100x, x200, 100×50, 100×200c50, 100×200c
Refer to <a href="http://fabrizio.zellini.org/resize-e-crop-immagini-in-php" title="Crop / Resize script" rel="nofollow ugc">This post</a> for more informations on resizer syntax.
PicGrab require Php version >=8, gd and curl libraries.

Picture grabber, resizer and cropper

Picgrab is a plugin that download, resize and crop an image on the fly. It also stores resized and cropped images in local cache.

benplum

Presswell

Presswell Art Direction gives editors and developers a consistent way to manage image sizing and cropping in WordPress. Define custom sizes, set focal points, and generate non-core thumbnails only when they are actually needed.
Features
<ul>
<li>Control image cropping with focal points</li>
<li>Define custom image sizes and nested thumbnail variants</li>
<li>Select custom image sizes directly in the WordPress editor</li>
<li>Dynamically generate non-core thumbnails on demand</li>
<li>Run batch regeneration from a dedicated Media tool</li>
<li>Use Endpoint Mode when filename-based 404 handoff is unavailable</li>
<li>Import/export size definitions and migrate legacy focal-point metadata</li>
</ul>
Focal Point Cropping
Set a focal point for Media Library images to control how custom crops are framed. Mark the visual subject once, and generated thumbnails stay centered on the correct area.
Custom Size Management
Use the settings UI to define and edit custom image sizes. Registered sizes become available when inserting images in the block editor and classic editor workflows.
Dynamic Generation + Endpoint Mode
Presswell Art Direction avoids generating every custom size at upload time. WordPress core sizes are generated normally, while custom sizes are generated when requested in templates or by URL.
If filename-based 404 image requests do not reach WordPress (common in some NGINX/server setups), enable Endpoint Mode (<code>/pwad-image/?id=...&size=...</code>). The plugin includes an automatic compatibility check in wp-admin.
Regenerator
The Regenerator screen (Media -> Regenerate Thumbnails) builds a queue and processes images in batches, with progress metrics and retry handling for failed jobs. You can choose exactly which sizes should be regenerated.
<h4>Documentation</h4>
Public APIs
pwad_add_image_size( $args )
<ul>
<li>$args (array) (required) – Keyed array containing <code>name</code>, <code>key</code>, <code>height</code>, <code>width</code>, <code>crop</code> (optional), and optionally <code>thumbnails</code> values.</li>
<li>Thumbnail keys are prefixed with parent’s key like <code>[size]-[thumbnail]</code>.</li>
</ul>
Example:
<pre><code>pwad_add_image_size( array(
 'name' => 'Square',
 'key' => 'square',
 'width' => '1200',
 'height' => '1200',
 'crop' => true,
 'thumbnails' => array(
 array(
 'name' => 'Medium',
 'key' => 'medium',
 'width' => '800',
 'height' => '800',
 ),
 array(
 'name' => 'Small',
 'key' => 'small',
 'width' => '400',
 'height' => '400',
 ),
 ),
) );
</code></pre>
pwad_get_image_sizes()
Returns all currently-available sizes (WordPress defaults + plugin/theme sizes + Presswell Art Direction sizes/thumbnails).
Example:
$sizes = pwad_get_image_sizes();
pwad_get_image( $attachment_ID, $size_key, $attr = array() )
<ul>
<li>$attachment_ID (int) (required) – ID of image attachment</li>
<li>$size_key (string) (required) – Image size identifier (<code>thumbnail</code>, <code>large</code>, <code>my-size</code>, <code>my-size-mobile</code>, etc.)</li>
<li>$attr (array) (optional) – HTML attributes passed to the rendered image element</li>
</ul>
Returns an image tag.
Example:
$square_large = pwad_get_image( $img_ID, ‘square’ ); 
 $square_small = pwad_get_image( $img_ID, ‘square-small’, array( ‘class’ => ‘hero-image’ ) );
pwad_get_image_src( $attachment_ID, $size_key )
<ul>
<li>$attachment_ID (int) (required) – ID of image attachment</li>
<li>$size_key (string) (required) – Image size identifier (<code>thumbnail</code>, <code>large</code>, <code>my-size</code>, <code>my-size-mobile</code>, etc.)</li>
</ul>
Returns a keyed array containing the <code>file</code>, <code>url</code>, <code>path</code>, <code>height</code>, <code>width</code>, and <code>mime-type</code> values.
Example:
$square_large = pwad_get_image_src( $img_ID, ‘square’ ); 
 $square_small = pwad_get_image_src( $img_ID, ‘square-small’ );
Actions
pwad/image_generated
Fires immediately after a custom crop file is generated so themes/plugins can queue optimizers or post-processing.
Arguments:
<ul>
<li>$data[‘attachment_id’] (int) – Attachment ID.</li>
<li>$data[‘size_key’] (string) – Requested size key.</li>
<li>$data[‘size_data’] (array) – Registered/requested size definition used for generation.</li>
<li>$data[‘source_file’] (string) – Source file path from attachment metadata (relative upload path).</li>
<li>$data[‘generated_file’] (string) – Generated filename for the new crop.</li>
</ul>
Example:
add_action( ‘pwad/image_generated’, function( $data ) { 
 // Example: queue optimization when a new crop is created. 
 if ( ! empty( $data[‘attachment_id’] ) && ! empty( $data[‘generated_file’] ) ) { 
 do_action( ‘my_optimizer/queue’, $data ); 
 } 
 } );
WP-CLI
wp pwad regenerate
Regenerates thumbnails.
<ul>
<li><code>--queue-per-page=<int></code> (default <code>200</code>)</li>
<li><code>--batch-size=<int></code> (default <code>25</code>)</li>
<li><code>--target-seconds=<float></code> (default <code>5</code>)</li>
<li><code>--resume-last=<0|1></code> (default <code>0</code>, continue the last interrupted queue)</li>
</ul>
wp pwad cache-prime
Generates thumbnails based on sitemap.
<ul>
<li><code>--sitemap=<url></code> (optional, auto-detects from robots.txt/common sitemap endpoints)</li>
<li><code>--page-limit=<int></code> (default unlimited)</li>
<li><code>--image-limit=<int></code> (default unlimited)</li>
<li><code>--delay-ms=<int></code> (default <code>250</code>)</li>
<li><code>--timeout=<float></code> (default <code>10</code>)</li>
<li><code>--retries=<int></code> (default <code>2</code>)</li>
<li><code>--include-external=<0|1></code> (default <code>0</code>)</li>
<li><code>--force-endpoint=<0|1></code> (default <code>0</code>)</li>
<li><code>--report-csv=<path></code> (optional, writes per-URL status/error report)</li>
<li><code>--dry-run=<0|1></code> (default <code>0</code>)</li>
<li><code>--resume-last=<0|1></code> (default <code>0</code>, continue the last interrupted prime run)</li>
</ul>
wp pwad cache-prune
Deletes cached thumbnails not referenced in sitemap.
<ul>
<li><code>--sitemap=<url></code> (optional, auto-detects from robots.txt/common sitemap endpoints)</li>
<li><code>--batch-size=<int></code> (default <code>200</code>)</li>
<li><code>--max-images=<int></code> (default unlimited)</li>
<li><code>--page-limit=<int></code> (default unlimited)</li>
<li><code>--image-limit=<int></code> (default unlimited)</li>
<li><code>--timeout=<float></code> (default <code>10</code>)</li>
<li><code>--grace-days=<int></code> (default <code>0</code>, uses file modified time)</li>
<li><code>--include-external=<0|1></code> (default <code>0</code>)</li>
<li><code>--force-endpoint=<0|1></code> (default <code>0</code>)</li>
<li><code>--report-csv=<path></code> (optional, writes per-file keep/delete report)</li>
<li><code>--dry-run=<0|1></code> (default <code>1</code>)</li>
<li><code>--resume-last=<0|1></code> (default <code>0</code>, continue the last interrupted prune run)</li>
</ul>
wp pwad cache-clean
Deletes all cached thumbnails.
<ul>
<li><code>--batch-size=<int></code> (default <code>200</code>)</li>
<li><code>--max-images=<int></code> (default unlimited)</li>
<li><code>--include-default=<0|1></code> (default <code>0</code>)</li>
<li><code>--dry-run=<0|1></code> (default <code>1</code>)</li>
<li><code>--resume-last=<0|1></code> (default <code>0</code>, continue the last interrupted clean run)</li>
</ul>
wp pwad queue-status
Shows resumable/remaining state for regenerator and cache queue runs.
<h3>Privacy</h3>
Presswell Art Direction does not send image data to external services. It processes image metadata and generated variants within your WordPress environment.

Presswell Art Direction

Really easy to use, and integrated perfectly with the front end of the site without any extra javascript or CSS required. Perfect add-on.

Very well done

Manage focal-point cropping and on-demand custom image generation in WordPress.

Picture grabber, resizer and cropper vs Presswell Art Direction