RustyBadRobot

Rusty Social Image Share resizes your post thumbnail to perfectly fit to the Facebook Share dimensions whilst keeping your original image dimensions.
See the <a href="https://wordpress.org/extend/plugins/rusty-image-share/screenshots/" rel="ugc">screenshots tab</a> for more details.

Rusty Social Image Share

Keep your original Featured Image proportions whilst sharing to Facebook.

Alex Mills

By default, WordPress uses the center of an image when creating cropped thumbnails. SmartCrop attempts to find and use the most interesting part of an image and centers the cropping on that portion of the image.
This process is entirely automatic and cannot be manually controlled. There are other plugins out there if you wish to manually specify where you want thumbnails to be cropped.
Since this analysis process can be slow on large images, thumbnails are initially center cropped and later asynchronously regenerated to be smartly cropped. This avoids the uploading of new images from being slow. The one side effect of this however is that your browser may load and cache the centered thumbnail before it’s re-cropped.
Want to smartly crop your past image uploads? You can use my <a href="https://wordpress.org/plugins/regenerate-thumbnails/" rel="ugc">Regenerate Thumbnails</a> plugin to trigger that. Make sure to uncheck skipping existing thumbnails.
<h4>Need Help? Found A Bug? Want To Contribute Code?</h4>
Support for this plugin is provided via the <a href="https://wordpress.org/support/plugin/smartcrop" rel="ugc">WordPress.org forums</a>.
The source code for this plugin is available on <a href="https://github.com/Viper007Bond/smartcrop" rel="nofollow ugc">GitHub</a>.

SmartCrop

Instead of cropping to the center of an image, SmartCrop attempts to use the most interesting part of the image for the thumbnail.

Rusty Social Image Share vs SmartCrop