The atmospheric Dear photographer website only underscores the transitory nature of digital photography

'Speechless. Tears. Read this," said a tweet in my Twitterstream. "This" turned out to be a website called Dear Photograph. It invites people to post pictures that incorporate photographs from their past taken in the locations featured in the original picture, much as people hold postcards of the Eiffel Tower so that the card obscures the actual view of the tower. It's a remarkably simple but powerful idea, and it does indeed evoke some of the responses mentioned in the tweet that brought me to the site. Here's a photograph of a smiling child. Behind her is a stocky man in a baseball cap, with his arms resting on hers. "Dear Photograph," the caption reads, "Dad is gone. but the strength of his arms will always be around us." It's signed "Holly".

Here 's another. It shows a couple sitting on a bench in the woods. It has an arm around the other. The caption reads: ".. I fell in love with a woman I 'm not ready to let go ... but it is"

A third image shows a crumpled snapshot of a woman in a 1940s outfit to walk along a street. "Dear Photographer," reads "If I could, in 1942 the corner and walk right into my mother, I 'd ask," Can I go next to you one more time? 'Love, Your Daughter. "

Another shows two children dressed in clown outfits. "We were inseparable for 26 years," says the caption, "to cancer came their way. Can you please give me back my sister?"

Not all photos are over the loss of a loved one. It 'sa picture of a young girl with a Hula-Hoop. "I wish I could hula-hoop, like I used to," says the caption.

Dear photographer is a remarkable demonstration of the power of simple, boring photos to evoke memories. Who ever has a shoebox of old prints found in an attic, knows this. They result pictures of us, as we unlined young, slim and innocent of our parents, carefree expressions and unfurrowed, carefree eyebrows, the holidays were once enjoyed is, once visited. Photographs freeze moments in time, reminds us who we were - and, by implication, who we have become.

Photographer but love is also a strong reminder of how vulnerable they become power of photography. There is, for one thing, the brusque, matter-of-fact, upfront Conditions of the page. "If you send us your materials," reads "dearphotograph.com grant you a nonexclusive, irrevocable, royalty-free license to use the work to be copied, used, sub-licensed, adapted, transmitted, distributed, published , displayed or \ any other way under our discretion in all media. " Or, in the famous internet meme adapt broken English, "are all your memories are \ to us."

It 's nothing new in this, of course. It also applies to the billions of photos that were posted on Facebook, under conditions that "You grant us a non-exclusive, transferable, sublicensable, royalty-free, worldwide license to all IP content use information you post on or in associated with Facebook (IP Licence). This IP license terminates if you delete your IP content or your account, unless your content shared with other users, and they have not deleted them. "

The other sobering thought of photo will love that the site is only possible because the relative resistance of analog photography. The pictures on the site are obviously digital, but they could only have been created with old photos. All of this, it will be very difficult, so something in 30 years 'time is to do.

The reason for this is that while digital technology is generally very good for photography as a mass medium, it also has the resulting images more fragile and fleeting. Of the billions of photos every year, the vast majority are only as digital files on the camera's memory card or on the hard drives of PCs and servers on the Internet "cloud". In theory - with the right back-up regimes and long-term organizational arrangements - this means that they could, theoretically endure for a long time. (And prove all the hard drives, after all) in practice, given the vulnerability of storage technology, the speed is with the computer kit obsolete and change storage formats, and the fact that most people 's Facebook accounts to die with them It is likely that most of those billions of photos will not long survive the ones they found.

That 's why Magnum photographer Martin Parr concluded his take magnificent piece last year for a better vacation photos with a simple piece of advice: you print your images. "We are in danger," he wrote, "of an entire generation who has no family albums, because people simply leave them on the computer, and then suddenly they are deleted." He ' s right.