Well, I have tested a bit with the "Sync center" of Windows 7 and it works on the basis of "Offline files".
This is a bit different than the sync options of 3rd party tools.
I'll explain the difference.
With 3rd party tools usually there are two identical folders on both machines.
In your case that would mean, first copy the whole folder with pictures to the other computer, and then setting up a sync relationship.
And set the direction it has to synchronize in, and what to do with duplicates etc.
With Windows 7 it goes like this:
You have to activate offline files, and reboot.
Then you can browse your network computer, select the folder that you want to be able to use offline, rightclick it and select "always available offline"
Now when you are indeed working offline, your Windows 7 computer will remember the changes.
As soon as the other computer is started up, the Windows 7 comp will apply the changes you made (synchronize). that can be edited files, but also new files you added, or files you deleted.
The upside of this method is that you won't lose the space of the files on both computers, only on the parent computer.
The downside is that you don't really have duplicates of the files.
From what I understand your purpose is to have a second (backup) set of the files because you are afraid to lose them in case of disk failure.
If that is the reason, then I recommend using a 3rd party synchronizer.
A couple of months ago, I installed a very simple to use 3rd party tool at someones computer.
If you are interested I'll look it up.
Hope this was helpful