linal

Provides the ability to set a maximum width or height an uploaded image can be, if the image is larger than the specified values then it resized. Ideal for users who wish to upload multiple files without having to resize them via Photoshop or GIMP first.

Resize on Upload

Provides the ability to set a maximum width or height an uploaded image can be, if the image is larger then it is resized.

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

Resize on Upload vs Resize at Upload Plus