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.

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.

Resize at Upload vs Resize on Upload