Creating Disk Image of OS, and Updating Image After the Fact.

Ok, Here is my quandary…

We have 12 computers, each are identical, except for some specialized software that may go on one computer, and not another, that I can install manually.

What I am looking to do is to is update the machine to the latest rev of software, OS, etc… and then take a snapshot via building a disk image of the HD at the state it is in.

What my question is, is there a way to update the disk image’s OS, and software in said disk image, instead of having to rebuild the disk image every time there is an update?

The reason for this really is so that I can use a program like Deep Freeze on each computer and have it view a disk image to restore to if a program has been altered, etc…