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

huiz

The plugin affects the uploaded image while it is uploaded. Straight 
after it is uploaded, it it resized physically to the given width. 
There is no original image left, nor made a backup. Also EXIF infor- 
mation is lost.
A lot of WordPress users or developers who use WordPress as a CMS 
and want to configurate it for easy use, would like to have an option 
to resize uploaded images. Some images come straight from digital cameras 
and exceed 4000 pixels in width. So it would be nice to reduce that to 
the max width you use inside your WordPress theme.
If you want to keep control about perfect sharp and resized images, you 
better use photo editing tools on your computer, not a script like this.
The plugin uses a class originally from Jacob Wyke (www.redvodkajelly.com).

Resize at Upload

This plugin resizes uploaded images to a given width.

Resize at Upload Plus vs Resize at Upload