The site has a resizable editor that lets you either upload the image that you want to have used or supply the URL where such an image can be found, and then adjust it manually by changing its width, height and position. A preview window will let you see the effect of all these changes in real time.
Spritebox can be used for free, and there is no need for you to sign up in advance either. The site is usable on the fly – as long as you have any of the browsers mentioned above, then you will be able to start turning your images around.
Spritebox.net In Their Own Words
Create CSS from Sprite Images.
Why Spritebox.net It Might Be A Killer
It is a free tool that can let designers save a considerable amount of time when it comes to processing images and having them turned into CSS classes and IDs.