Greg - SiteOrigin

A lot of themes ship with Timthumb because it allows their users to start using the theme without rebuilding thumbnails.
Secure Image Resizer offers a far more secure alternative. It allows theme developers to rely on WordPress’ own image resizing functionality using <code>add_image_size</code> and <code>get_the_post_thumbnail</code>.
When get_the_post_thumbnail is called, Secure Image Resizer checks if the requested image size exists. If the image doesn’t exist it dynamically creates the resized version. It works in the background, with no front end functionality.
Theme developers can either bundle this plugin into their themes, or suggest that their users install it.
It also includes 2 functions <code>so_resize_custom</code> and <code>so_resize_custom_html</code> to do dynamic image resizing using Imagick. Great for theme developers.
Please Note: This is an early release of Secure Image Resizer. Please use it, try and break it and report any bugs to me support@siteorigin.com so I can quickly fix them and work towards version 1.0.

Secure Image Resizer

A very simple and secure image resizer. It adds dynamic resizing so you don't need to regenerate thumbnails when you install a new theme.

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.

Secure Image Resizer vs Resize at Upload