puggan

You just uploaded a few images to you blog, and notice that the thumbnails cut off the heads of them, 
here is a tool to specify exactly how you want your thumbnails cut, you can zoom in and drag the thumnail 
area to the position that you want. 
This tool is even more useful in combination with theams and plugins that use of thumbnails.

Reposition Thumnails

A pluggin for the moments when the center of the picture wasn't that good as thumnail, so you can avoid cut of heads in yout thumbnails.

mansoormunib

Image Sizes in Admin Dashboard adds a read-only widget to the WordPress admin Dashboard that lists all currently registered image sizes.
Any size you register in your theme or plugin with <code>add_image_size()</code> is picked up automatically, alongside the built-in <code>thumbnail</code>, <code>medium</code>, <code>medium_large</code> and <code>large</code> sizes. Each row shows:
<ul>
<li>The image size name (human readable)</li>
<li>Width in pixels (— when unconstrained)</li>
<li>Height in pixels (— when unconstrained)</li>
<li>Crop mode (Cropped or Proportional)</li>
</ul>
This is handy when building a theme and you need a quick reference of the exact dimensions available to <code>the_post_thumbnail()</code> and the media library.
More detail on registering custom image sizes: https://developer.wordpress.org/reference/functions/add_image_size/

Image Sizes in Admin Dashboard

....

Lists every registered image size — built-in and custom add_image_size() sizes — with width, height and crop mode in a Dashboard widget.

Reposition Thumnails vs Image Sizes in Admin Dashboard