Sharing a single iphoto library and backing up with time machine

Question

Alright,
I want to share my iPhoto library between several users on my Mac. I have found an Apple article that explains how to set up a disk image to store the iPhoto library in. This article is at
http://support.apple.com/kb/HT1198
However, implementing as described in this article has a very painful disadvantage described below:
I back up Mac's my hard drive to an external disk using Time Machine. Once I've created a disk image to hold my iphoto library, time machine will now back up the entire iphotolibrary.dmg file each time I've added or changed any photos. Now I have a lot of photos, and my iphoto library takes up 27GB even when put on a sparse-disk-image. So that means that each time I add or change even just one photo, time machine has to write a >27 GB file to the external hard drive which contains my backup. Obviously this is a problem and will fill up even my 1.5TB drive pretty quickly if this continues.
I came up with an idea on how to solve this. I decided that I'd exclude the disk image that contains the common iPhoto library from the time machine backup and create a second library in the home directory of one of the users on my machine. Then each time that I added or edited photos I'd use a syncing application to sync the iPhoto library on the disk image and the iPhoto library in the user's directory. This way the iPhoto library in the user's directory would be backed up incrementally by Time Machine in the normal way, and Time Machine wouldn't fill up the backup disk with huge disk image files that have only changed slightly.
The problem with my new approach is that the snycing program that I'm using (Synk by Decimus Software) has some difficulty syncing the packaged directories like that used for iPhoto libraries. I get all sorts of conflicts and I'm worried that the file syncs will be unreliable and lead to instabilities and data loss.
An ideal solution would be exclude the disk image file from the Time Machine backup and then add the mounted disk image to the backup. I think that Time Machine would then correctly leave the large 27GB file alone and only do incremental backups of my iPhoto library. But I can't see any way to add mounted disk images to the Time Machine backup.
Thanks in advance for any help that any of you can provide.

Answer 1

This is a little more simple that all that.
For iPhoto 09 (version 8.0.2) and later:
If you want the other user to have the same access to the library as you: to be able to add, edit, organise, keyword etc.
Quit iPhoto in both accounts. Move the Library to the Users / Shared Folder
(You can also use an external HD set to ignore permissions, a Disk Image or even partition your Hard Disk.)
In each account in turn: Double click on the Library to open it. (You may be asked to repair the Library Permissions.) From that point on, this will be the default library location. Both accounts will have full access to the library, in fact, both accounts will 'own' it.
However, there is a catch with this system and it is a significant one. iPhoto is not a multi-user app., it does not have the code to negotiate two users simultaneously writing to the database, and trying will cause db corruption. So only one user at a time, and back up, back up back up.
No need for dmgs at all. No need for Syncing software.
Note: No Syncing software can run on an iPhoto Library. Period. There is none that can parse the Library database. Attempting to sync two Libraries will lead to damage to at least one of them.
Regards
TD