How should I image a hard drive in a platform independent and future-proof manner?

What methods of producing hard drive images stand out with regards to being platform independent and standing a good chance of usability in the future. Some considerations:

1. Can the imaging program be run on a variety of OS, disk, paritition, and file system types?
2. Can the image by mounted in place by a variety of OS's?
3. Compression would be a plus, as well as actual files vs. bit for bit copying.

The motivation for my question is having old hard drives that I must hang onto and wanting to make sure that I have backups of them just in case as well as to use the images as an easier access mechanism versus actually having to hook them up to some computer with the disk's specific hardware interface. I also regularly use OS X, Linux, and Windows OS.

I've searched superuser and while there are similar questions, I don't see a duplicate that address these specific aspects of imaging hard drives. If I'm wrong, please add the appropriate link.

This question assumes you're going to be "burying the backup in the ground until you need it" which is never a good backup solution. The simplest way to future proof things like this is to periodically migrate them to newer systems. This is good idea anyway since you're probably going to run into hardware problems with your older backups before you ever run into software compatibility problems. Just use imaging software that's made by a major company that you can be reasonably certain won't go out of business. Or go open source and backup a copy of the source code too.

Something I'm doing for a client sort of addresses these needs. We'll be using VirtualBox.org to make it usable in the future...

Step 1: Create a VirtualBox.org computer, with adequate disk space

Step 2: Install the needed OS (in this case, Windows XP) and all its updates

Step 3: Install the contact management software they may need for the next 7 years (as required by federal tax laws here)

Step 4: Restore a backed up copy of the data files (and verify that it all works)

Step 5: Reboot the virtual computer to make sure it's all still working

Step 6: Shut down the virtual computer and make a copy of the file to one or more external hard drives

Step 7: Copy the VirtualBox.org installer to the external hard drive(s)

Now, what we're assuming here is that VirtualBox.org is going to be available in the future for whatever OS is being used at that time so that if the version of its installer that we included on the hard disk isn't compatible with newer OS in the future, then we can simply install the newest version that is [expected to be].