If you own a digital camera then no matter wheter you take pictures to record memories of your holidays, as a hobby, or as a professional, you are likely going to want to keep your photographs safe from harm. Most people when they get back from a trip they will transfer their photographs from their Flash media to their computer. An increasingly common practice is to leave your photos on the card past this point until a time when you need to use the card again. This does offer some redundancy for you to fall back on should your hard drive fail - but it's a very temporary solution and is not practical once your photos start taking up many gigs of space. This is when you should start looking at alternative ways of backing up.
If you live in a hosehold with multiple computers then the easiest and most readily available solution is to transfer copies of your photos to these other systems. Even if you have an iPad this it will have enough space to backup some photos to. The main problem with this method though is that if your photographs start running into the tens or hundreds of gigabytes then that is a lot of storage space used on each machine.
Pros: Quick and easy to do using readily available hardware
Cons: Cumbersome, and can be impractical if storing a lot of photos
If you have a pro account with Flickr (costs $47.99 for 2 years) then an easy method of backing up selected photographs is to upload the full size versions to Flickr. If you don't want the full-size version to be available then this creates the extra steps of ensuring your full-size version is hidden to all and then uploading a smaller public version of those you want people to be able to view.
This method does worry some people as with Yahoo's recent closures of long running services such as MyBlogLog some feel that Flickr is not safe and could be closed down by Yahoo with very little warning. Personally I see this as unlikely, but I do find this method of backing up to be too cumbersome. I upload the full-sized version for photographs I make publicly available and this acts as a last ditch effort should any of my other backups fail.
Pros: Relatively cheap
Cons: No easy way of recovering your photos to use locally if you need to recover hundreds (or thousands)
Dropbox and The Cloud
There is a lot of noise lately about using the so-called "Cloud" for storing your files. The idea of this is that services such as Amazon EC2 or Dropbox could be used to back your files up to. With Amazon EC2 you pay for what resources you use and depending on what Tier you use will depend on how much you pay. They do however have a free tier that offers 750 hours of instance usage, 750 hours of load balancing with 15Gb of data processing, and 15Gb of bandwidth. I can't help but think that using the EC2 method could end up costing far more over a year than the other methods which is why I use Dropbox. With Dropbox you install software on pretty much any device you want - your iPhone, Mac, Windows machine, etc. and it can automatically sync files from a folder to the cloud. The pricing of Dropbox is based upon the space you use - which with a lot of photographs could actually be quite a bit. The basic of their plans is free and allows 2Gb of usage, though it will increase by 500Mb for every referral you make. They then have a 50Gb plan for $9.99/month and 100Gb for $19.99/month (yes it's $0.01 cheaper to buy two 50Gb plans!). This means you'd be spending around $119.88 or $239.88 a year based on how many photographs you want to keep backed up. Over 5 years this would get quite expensive and so whilst it is safe as an "off-site" backup it doesn't offer the best value for money.
When it comes to cloud based storage the playing field is changing quickly with many other possibilities with prices and plans that change quite quickly. One that's been around about as long (if not longer) than Dropbox is "box" which offers 5Gb of storage for free and up-to 50Gb of storage for paying personal customers. They also have business and enterprise levels that offer far more storage space if you need it. Amazon CloudDrive also offers 5Gb of storage for free, though by buying an MP3 album from their store and sending it to your CloudDrive you get upgraded to 20Gb storage for free for one year.
Pros: Provides secure off-site backups
Cons: Can get pricey quite quickly
Portable HDD (Time Machine)
A portable solution is to use a USB HDD which is a one-off purchase and can be carried around with you should you need it. The problem with these though is that they are not as resilient as some of the other solutions. Over the past 10 years I've gone through about 4 laptop sized hard drives and about 3 casings for them due to malfunction - each time the contents of the drive has been lost. This means that whilst it's an easy solution that just requires a trip to your local PC World or other store, it is far from being a safe backup solution. Outside my own personal experience of using these for backups I know a lot of people that use Western Digital "My Passport" drives where a lot where bought at the same time. About 40% of them died shortly after their first year of being used in conjunction with Apple's Time Machine software.
Pros: Widely available, easy to use
Cons: Not as resilient as other backup solutions
Network Attached Storage is probably the most durable and hardcore of these solutions and can be used in a variety of ways. My preferred method is to use the RAID array of a NAS in a mirrored mode (RAID 1) so that there are multiple copies of an image should one of the HDDs die. If you have more than 2 drives though then there are other RAID levels available that can offer better fault tolerance. For example, the hybrid RAID level 1+0 could be used if you have a minimum of 6 drives and would be the most tolerant of the RAID arrays, but is also the most expensive to implement as across the even number of drives you use you would lose more than half of the capacity.
I use a NAS as the primary location for my photographs so that iPhoto / Aperature on the Mac can be pointed at it to use as it's library and I can still easily access them from my PC or transfer them to an iOS device. If you prefer to keep your working copies of photographs locally then you will still need to either manually transfer backups to the NAS or have an automatic / scheduled way of achieving this. Forgetting to backup is just as bad as not having a backup method so it really is worth thinking the process through also.
The Synology DS211 is a good 2-bay NAS enclosure (no drives) you can get for around £223 and has decent firmware installed. This one is more or less a middle-of-the-road NAS solution as you can get them for quite a bit cheaper and for considerably more. One popular NAS solution is the Drobo by Data Robotics which comes in a variety of models, though from what I can see, the cheapest of the network models, the Drobo FS is currently retailing at £520 for a 5-bay enclosure (no drives). A lot of NAS solutions will allow you to configure them as webservers, etc. and will be configurable via a web interface.
Pros: Highly resilient, adaptable to different requirements
Cons: Expensive in the short-term