sharespring

Image resize service for web dev. 
Let our servers crop, compress, and deliver your images. 
Save time. Improve page speed. Crop automatically. 
Define image sizes in code and display everything at the right dimensions. 
We think this is how all sites should render images.

SwiftPic

Helper functions for image resizing in theme development using SwiftPic. https://swiftpic.io/

MagicAce

This plugin permits you to scale images up, as well as down, in the default WordPress media editor.
Scenario 
You have a site/blog with most content as 640×480 images (or whatever size you use). But now, for whatever reason, you want to add a 480×360 image to your site and you wish to upscale it to 640×480 so the size matches everything else and doesn’t look out of place..
Problem 
Using the default WordPress media editor, you are only permitted to scale down images, not scale up. Without this plugin, your only options would be to edit the image externally (Photoshop, etc.), or figure out another solution using percentages.
Solution 
Install & Activate this plugin! Now, using the default WordPress media editor, you can upscale as well as downscale your images without any hassle!
A working and simple solution.

Scale It UP!

This plugin permits you to scale images up, as well as down, in the default Wordpress media editor.

SwiftPic vs Scale It UP!