Apple offers .Mac subscribers a free and simple backup utlility, called Backup. In my experience it isn't always 100 per cent effective, but even when the software fails to fully restore your data there's a clever trick that should help you grab back the information you're missing.

This cropped-up this weekend. My partner was attempting to reclaim some space on her hard drive. She's a photographer who particularly enjoys capturing images at live music events and festivals, and she's beginning to make a bit of a name for herself.

So, she likes to use iPhoto as her media browser/file manager for her images, reserving Photoshop for advanced image editing on those images she sells (and I'd love for her to have a copy of Aperture, but this hasn't happened as yet).

Thing with iPhoto is the way it manages files: it's a non-destructive image editor, so it retains a copy of the original image - but also keeps copies of each edit applied to that image within the application.

This means you can end up with multiple copies of an image stored at various places across the hard drive. Thing is, the only pictures you'll see in iPhoto are the original and final edit. This means you lose a great deal of hard drive space which is dedicated to holding those in-between edits.

iPhoto desperately needs a way a Mac user can easily remove those surplus images, but we haven't found an effective solution yet - don't forget, for my other half those images are too important to take risks with.

But, eventually, she did, zapping the library to just reinstall those images she most needs.

Preparing for this, over a period of time she used Backup to create backup archives of her image collection on an external hard drive. She also (irregularly) maintained a duplicate of the iPhoto Library on that drive, and attempted to burn CDs of each fresh image collection as she completed work on it. A good triple backup strategy, we thought.

Apart from human error...

When she zapped her iPhoto Library this weekend, she was shocked to discover that she'd neglected to update the copy of the library on the hard drive. She also found she'd forgotten to burn CDs of one particular image collection.

What made that worse is that this collection was one she recently found a client for - and was making drive space on her Mac in order that she could do some advanced Photoshop editing work on some of these images.

In a crisis, we turned to Backup and hit the Restore button. And that's when Backup failed.

She'd lost the pictures. But those Backup files were still there - surely there was something in them. How do you open a Backup file to get the data you need back out of them?

Here's what we did to get them back:

1/ In a new Finder window, navigate to the Backup folder on your external drive.
2/ Control-click on the incremental Backup files one at a time.
3/ In the pop-up contextual menu that appears navigate to and select the 'Show Package Contents" command.
4/ In the folder you find yourself in, select and open the folder called Contents.
5/ Then go to the next folder you see there, which is also called Contents.
6/ You'll find a Disc Image file here.
7/ Drag that file to your Mac desktop, click on it to mount it.
8/ Inside you'll find a mass of folders - in this case the filing system iPhoto creates, with a plethora of not particularly helpfully-named folders.
9/ Then, folder by folder, ferret through the files looking for the high-resolution images (or other data) you are looking for.

It took ages, but we found most of the folders in the end. Those we didn't find were mostly tracked down using Prosoft's excellent Data Rescue II software, but that, dear reader, is another story.