“ISO Creator” is the best option for creating an ISO or image of Operating System Binaries. Assuming the OS DVD is available, and you are in a situation where you need to quickly get a Server OS up and running, and need an ISO [because it is bootable], then ISO Creator is one of the easiest and reliable. It is one of the most popular Windows related software downloads. And, it is free.
Stick the DVD in the DVD drive, then open the software, point it to the proper locations. So, below, it was the Server OS on a DVD drive, and the destination local folder.
This is all there is to it, although the process can take some time.
All done, after about 25 minutes.
The man’s most humble of web sites [it’s a compliment] has all the goods needed.