How do I "image" a hard drive?

First to answer your question: to create a hard disk image, you'll need a disk imaging utility. There are several, though as I mentioned I don't use one, so I don't have a real recommendation. These utilities will walk you through the process of creating an image.

Now, why don't I use one?

Most people think of disk imaging as a backup utility. As you've pointed out, if you "mess things up", you can restore the system to the original state that it had at the time you took the image. The problem is that the image is monolithic - all or nothing. That means any and all changes you've made since making the image will be lost when you restore. All of them.

Now, I don't know about you, but while I do "mess things up" on a regular basis, I also do many, many other things that I don't really want to lose. So for me the approach to restoring from a full disk image would be to first try to copy off the data that I want to preserve, hope that I got it all, restore the image, and then restore the data. That seems like a fair amount of work to me.

My approach is slightly more traditional: an incremental backup solution. It backs up things as they change.

And yes, when things get really messed up, I rebuild my machine. From scratch. What I find, though, is that because I install and uninstall software on a fairly frequent basis, about every two years or so I need to rebuild the machine anyway.

So when does disk imaging software make sense?

The single biggest use for imaging software is in corporations, where large numbers of machines need to be built out frequently, and identically. Rather than running through the setup for Windows and whatever other applications might be part of the standard configuration over and over for each machine, it's done once, and then imaged. That image can then be restored onto multiple hard disks significantly faster than the standard setup process.

Another use for disk imaging software is for benchmarking and software comparison tests. When comparing several different utilities, the only valid comparison may be to start from an identical configuration each time. A standard disk image of the system provides a quick and easy way to start from an identical state each time.

And yes, a disk image tool might sometimes be used in conjunction with an incremental backup strategy.

But after all is said and done, to me a traditional backup strategy seems just as much work, and slightly more flexible.