mores

This plugin is basically just a little improvement of <a href="https://wordpress.org/extend/plugins/resize-at-upload/" title="Resize-At-Upload" rel="ugc">Resize-At-Upload</a>, a fabulous plugin by A. Huizinga.
The plugin will automatically resize an image upon upload, depending on the maximum width and height that you define. Gone are the days when you, or your client, will ruin a site’s layout by uploading a huge file with 25 megapixels. 
Be advised: there is no backup, no copy of the originally uploaded image.
The plugin uses a class originally from Jacob Wyke (www.redvodkajelly.com).

Resize at Upload Plus

Automatically resize (i.e. scale down) images after uploading. Save disk space and preserve your layout

ERA404

Extends the WordPress Media Library to allow individual control over each media item size’s crop.
For those particular about their imagery…
WordPress’s Media Library already gives authors strong, intuitive organization over their web site’s images. But some users are a little more particular than others over the individual crop sizes of each media item. CropRefine is for the keen-eyed, visual types who want something fast and fastidious.
<ul>
<li>CropRefine provides quick-links from the Media Library to refine each item.</li>
<li>A full catalog of existing crops and sizes are made available for refinement.</li>
<li>If you prefer a different/better thumbnail but want to leave the other sizes untouched, CropRefine gives you that level of granularity over your imagery.</li>
<li>Packaged with cropper.js, adjusting a crop is a smooth, draggable, precise refinement experience.</li>
<li>Iterative backups are stored alongside each adjustment, so nothing is ever lost—only gained!</li>
<li>If a re-crop just won’t achieve the results you’re after, a quick-upload tool is also offered for each media item size, so that you can replace that (and only that) size.</li>
<li>No additional database is needed, no exhaustive setup process, no hidden license costs.</li>
</ul>

CropRefine

Giving you greater control over how each of your media item sizes are cropped.

Resize at Upload Plus vs CropRefine