Digital images are much safer than negatives for one simple reason: we can easily and cheaply store multiple copies of digital negatives.

You do, though, need a good strategy for storing, archiving and backing-up your images.

Let's start with some definitions ...

Working storage: the place(s) the image is stored while you are working on it.

Archive: The main place you store images after you have done the post-processing.

Backup: One or more emergency forms of storage in case your main archive fails. I recommend at least two backups, in which case you have a primary and secondary backup.

Working storage is pretty simple. This will be on the hard drive of the PC you are using to do the processing. The only comment I have on this is to ensure that you always have more that one copy of the file you are working on, so if you do something stupid, you always have the option of starting again.

In my case, I always copy (and not move) images from the card to my laptop, so that the original image remains on the card. I only format the card when I next use the camera, which will be after I've finished post-processing the previous shoot.

For archive, there are two main options: hard drive and DVD/CD. So let's look at the pros & cons of each ...

First, let's eliminate one variable right away. All media can and do fail. Hard drives, CDs, DVDs, tapes ... all have a limited life, and all can fail without warning. No matter what medium you choose, you will always want at least one backup, preferably more than one.

Hard drives have the clear advantage when it comes to speed and convenience. The relatively low price of large-capacity drives makes it feasible to have your entire photo archive permanently and instantly available. Compare this with DVDs or CDs, where you must first physically locate the right disc, then load it, then copy the files across, and the benefit is obvious.

A second advantage of hard drives is that any failure is immediately obvious. Because you access it every time you take a new set of photos, if the drive fails, you will realise it immediately. At this point, you can replace it and copy the files across from your backup. In contrast, the first time you access a DVD or CD is going to be the first time you actually need the file: this is not a good time to discover that it has failed.

A third advantage of hard drives is that they tend to be replaced pretty regularly as capacities increase. My first ever hard drive, in 1983, was 5Mb (that's five megabytes, not gigabytes). That was replaced about a year later by a 20Mb drive. Currently I have a pair of 250Gb drives, and the replacement for those will almost certainly be 1Tb (one terrabyte = 1000Gb) drives.

When you replace a hard drive, you can copy across thousands of images by dragging and dropping a single folder. Compare that with the effort involved in re-archiving hundreds of separate CDs or DVDs ... it just doesn't bear thinking about.

So hard drives are likely to be replaced before they fail, while DVDs will simply sit there until they do.

The main advantage of DVDs and CDs, however, is their portability. For off-site storage in particular, you can simply take them somewhere and leave them there.

For backup, there is a third option: online backup services (links to a page in my Gadgets section). The big advantage of these is that they are fully automated, so they don't rely on good intentions.

This to me makes the choices pretty obvious ...

For your archive, only a hard drive makes sense. DVDs and CDs are just too fiddly and time-consuming, and any failure will go undetected until the image is needed.

For primary backup, I would again say a hard drive makes the most sense - because it is tested every time you backup a new set of images, and because it will be replaced regularly.

For secondary backup, the key criteria is that this is physically located in a different location to the primary backup. If your home or office burns to the ground, it doesn't matter how many copies you have if they were all in the building. (A fire-safe may protect your files, but I wouldn't count on it.) This means either DVDs stored elsewhere (home/office/friend) or a remote server.

I use my laptop for working storage, external hard drives for archive, external hard drives for primary backup and an online server for secondary backup.

Note that DVD writes can and do fail, so always select the verification option to ensure that it was written correctly. A hard drive failure, with the loss of your photos, is not the time to discover that your secondary backup is toast.

The final issue you may like to consider is the risk of losing photos before you get back home/to the office. The chances there are extremely low, but if the photos are important (eg. a commercial shoot, wedding or a destination you're unlikely to visit again), an on-site backup does give that extra peace of mind.

Many people use ImageTank type devices: a card reader with built-in hard drive. Insert a card, and the images on it are automatically backed-up. Some of these devices also have colour displays so you can review your images.

Personally I carry a small laptop in my camera backpack. This has a couple of advantages. First, when travelling, I have the ability to process the images on the move as well as store them. Second, I can create an additional backup by copying the files from the laptop to a USB key or mobile drive.

Ridiculous paranoia? Well, maybe - but the one weakness with the ImageTank solution is that you almost certainly carry it in your camera backpack, as I do my laptop. If that is stolen, your backup disappears with the originals. A USB key or external hard drive can be carried in a pocket.