Often an off the shelf CMS will have native functionality, or a plugin, for doing something like this. There are editors you can use like CK Editor, but I don't think you can crop and resize images like that. So what you want is a plugin that can be integrated into any CMS that has this feature.
A quick Google brought up JCrop, a jQuery script that it seems you can use for this purpose.
This is the site: Jcrop - Deep Liquid
And here's a video demo: jCrop Demo
I'm sure there must be more options out there, though.