Deleting original image files after upload

I am wondering if there is any way to stop WordPress storing original uploaded images on the server?

Some of our clients original images are up to 8MB in size – WordPress does a great job of resizing them for max/med/thumbnail sizes, but still keeps the original images in the uploads folder. Our wp-uploads folder is now absolutely enormous (very image-heavy site)!

Short of resizing every image in Photoshop beforehand (time-consuming and hard to explain to a non-computer-savvy client!), is there a simple way to stop WordPress storing the original upload, or maybe some kind of “purge” plugin?

Thanks