Research by the online storage firm revealed that on average Brits have 1500 digital snaps or videos stored on their PC, but one in five admit they don't bother to back them up.
A quarter of PC users said they only back up data to a CD, USB or external hard drive.
Mozy said those that had lost their digital snaps had, on average, lost four years of memories, with holiday snaps, baby photos and pictures capturing special occasions such as birthdays, weddings, anniversaries and graduation ceremonies the most commonly lost photos.
Furthermore, two thirds of PC owners don't back-up any of the music files on their PC, despite the fact 15 percent admitted they had lost their digital music collection in the past.
Mozy also said the average estimated value of all data stored on a PC is a whopping £12,484 (US$18,675) per machine. The online backup firm said that's 2500 times the monthly cost of protecting it online
"People think that backing up to CDs, USB keys and external hard drives is enough to keep their data safe but, whilst this is great way to get your data back quickly, it's still at a massive risk of loss," said Claire Galbois-Alcaix, of Mozy.
"Backing up to this sort of device can work perfectly if your computer fails but, if your laptop has been stolen or soaked by a burst water pipe, local backup typically falls foul to the same fate as the computer: in a house fire, a CD is just as likely to melt as a PC. That's why a backup service that automatically makes a copy of your data locally as well as storing it securely online is such a good idea."
The research also revealed that 42 percent of Brits would save a computer from a fire but only 29 percent would save their family heirlooms, which are passed down from generation to generation.
See also: Mozy UK Online Backup
This story, "Lost a Digital Photo? You're Not Alone" was originally published by PC Advisor (UK).