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.

Presswell

benplum

Presswell Art Direction helps simplify how custom image thumbnail sizes are defined, cropped, and generated.
Features
<ul>
<li>Control image cropping with hot-spots</li>
<li>Select custom image sizes in the WordPress editor</li>
<li>Dynamically generate image thumbnails</li>
<li>Delete all cached thumbnails</li>
</ul>
Image Cropping
Presswell Art Direction adds the ability to set a focal point hot-spot for all images in the media library for fine grain cropping control. Simply identify where the subject of the photo is and the plugin will crop all custom image thumbnails to ensure it stays in frame.
Thumbnail Sizes
Presswell Art Direction adds an easy to use interface for defining and editing custom image thumbnail sizes. Custom image sizes will be available for selection when inserting images in the post editor.
Dynamic Images
Presswell Art Direction prevents custom image sizes from being generated automatically. Only standard WordPress thumbnails will be generated when a new image is uploaded. All other image sizes will be dynamically generated when called via code or requested via URL, saving server space when many custom image sizes are defined. Note: URL based image generation requires that <a href="https://codex.wordpress.org/Using_Permalinks" rel="nofollow ugc">pretty permalinks</a> are enabled.
<h4>Documentation</h4>
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>, and optionally <code>thumbnails</code> values; Thumbnail keys are prefixed with parent’s key like ‘[size]-[thumbnail]’</li>
</ul>
Example:
<pre><code>pwad_add_image_size( array(
 'name' => 'Square',
 'key' => 'square',
 'width' => '1200',
 'height' => '1200',
 '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( $attachment_ID, $size_key, $thumbnail_key )
<ul>
<li>$attachment_ID (int) (required) – ID of image attachment</li>
<li>$size_key (string) (required) – Image size identifier; Overload using ‘[size]-[thumbnail]’ pattern</li>
<li>$thumbnail_key (string) (required) – Image size thumbnail identifier</li>
</ul>
Returns an image tag.
Example:
<pre><code>$square_large = pwad_get_image( $img_ID, 'square' );
$square_medium = pwad_get_image( $img_ID, 'square', 'medium' );
$square_small = pwad_get_image( $img_ID, 'square-small' ); // Overloaded
</code></pre>
pwad_get_image_src( $attachment_ID, $size_key, $thumbnail_key )
<ul>
<li>$attachment_ID (int) (required) – ID of image attachment</li>
<li>$size_key (string) (required) – Image size identifier; Overload using ‘[size]-[thumbnail]’ pattern</li>
<li>$thumbnail_key (string) (required) – Image size thumbnail identifier</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:
<pre><code>$square_large = pwad_get_image_src( $img_ID, 'square' );
$square_medium = pwad_get_image_src( $img_ID, 'square', 'medium' );
$square_small = pwad_get_image_src( $img_ID, 'square-small' ); // Overloaded
</code></pre>

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

Control how custom image thumbnail sizes are defined, cropped, and generated.

Picture grabber, resizer and cropper vs Presswell Art Direction