Web images to get expiration date
German researchers have created software called X-Pire that gives images an expiration date by tagging them with an encrypted key.
Once this date has passed the key stops the images being viewed and copied.
Creators plan to levy a small charge to use the tagging system and put a digital lock on digital pictures.
"More and more people are publishing private data to the internet and it's clear that some things can go wrong if it stays there too long," said Professor Michael Backes of the Information Security and Cryptography department at Saarland University, who led development of X-Pire.
Dr Backes said development work began about 18 months ago as potentially risky patterns of activity on social networks, such as Facebook, showed a pressing need for such a system.
"Many people join social networks because of social pressure," said Prof Backes. "They tend to post everything on the first day and make themselves naked on the internet."
"Only a small fraction of people are active every day," he said. "The majority are passive users, they do not contribute apart from their initial phase and afterwards they do not seem to care or perhaps they just forget."
However, he said, social networks never forget and images posted to sites, be they embarrassing or not, were visible forever.
To help solve this problem, the X-Pire software creates encrypted copies of images and asks those uploading them to give each one an expiration date.
Viewing these images requires the free X-Pire browser add-on. Currently only a version that works with Firefox is available. Those without the viewer will be unable to see any protected image.
When the viewer encounters an encrypted image it sends off a request for a key to unlock it. This key will only be sent, and the image become viewable, if the expiration date has not been passed.
Images given an expiration date with X-Pire have been successfully uploaded to Flickr, Facebook and many other websites, said Prof Backes.
This testing was essential because the different ways that sites treat uploaded images added lots of complications.
"Facebook, for instance, does a huge amount of post-processing and whatever protection you deploy has to cope with that treatment," he said.
The X-Pire program should be available in late January and will cost 2 euros (£1.68) a month. Those who stop paying will not see their images suddenly become viewable, he said, instead they will just not be able to put expiration dates on new images.