http://www.backup-utility.com/free-backup-software.html
I keep the images on the second hard drive in the same machine if available.
Hirens, for example, has Backupper. I only use Backupper to save a system backup so I don't normally need to access inside for individual files. The free version no longer allows this. You can search for the "technician" version PE ISO and find it if needed.
Info below feels outdated.
AOMEI allows you to make a boot rescue ISO. I keep that on the same folder as the backups. When the PE environment is made from the same machine you are going to boot to, it might make a difference. For instance you can choose from legacy or UEFI boot. I had it offer to install specific drivers on certain machines.
If I try keeping the ISO somewhere else I will never be able to keep track of it. In the worst case I can always build another boot disk on another machine and probably get it to work.
A couple reminders:
1. AOMEI must be started as admin to attach the image if you wish to view or manipulate the image.
2. System backup only creates an image of the OS partitions. If you have moved your user files, you will need to back them up separately.
