Easiest way to routinely revert to a saved disc image?

I'd like to create an image of a mostly clean install of Windows 7 (only security software and other staple things included), be able to save it to that computer's HDD, and revert to it on a weekly basis. What's my best option for this?

As to my purpose, this is a computer that's going to be passed between many different people, most of whom are a liability when it comes to the health of a computer. However, the laptop itself doesn't require anything be saved on it, so is resetting it in this fashion on a weekly basis poses no inconvenience. Would this be an effective method for making sure nothing malicious can take root for any significant period of time?

Edit: to be clear, I'm looking for something that requires no external media. The limitation that seems to exist with some programs is that you can't back up from an image that's on the drive.

 

What happens in a few months when your system is missing all kinds of security patches? Are you going to run Windows Update each time you revert to the image?

 

Probably once a month. More if needed I guess, but creating a new image to load isn't particularly difficult.

 

I use clonezilla, but I don't think that allows you to save to the same drive the OS is on.

For patching updates I absolutely love wsuoffline. you run the Updategenerator and it downloads ALL patches for the specified OS. Then copy the client folder to the target computer and run Updateinstaller. It checks to see what patches the OS has and installs the needed ones with only 1 or 2 reboots.

 

I found a very simple solution. I simply partitioned the HDD, and saved the backup image to E:/, which allows me to use Window 7's native backup/restore functionality to load an image of C:/ from E:/

 

Just a tip:
When you make that system image, Windows keeps track of where it's stored and updates it regularly. This is something you may not want in this scenario. I don't remember if moving the image to a different folder is enough to prevent it from being updated, but IIRC moving it to a different partition did.