Showbiz news agency WENN is to start charging publishers for using pictures posted by celebrities on social media website Twitter.
WENN has signed a deal with social media firm Plixi, formerly called TweetPhoto, which is one of the largest online services used to post photographs on Twitter.
Those who post photographs on Plixi retain copyright of their images while signing over the commercial rights to sell on their pictures to publishers.
Under the deal announced today, WENN will enforce Plixi's rights to charge for the images and market them in the way it would any other images in its portfolio.
This means exclusive new photos posted by high-profile celebrities to Plixi could now be sold for tens of thousands of pounds to magazines, newspapers and websites.
WENN chief executive Lloyd Beiny said the new arrangement could bring an end to the "digital Wild West" which has seen publishers "liberally help themselves to photos posted on Plixi and reproduce them with scant concern for the ownership of copyright".
The agency will now monitor publications for unauthorised use of Plixi images and levy charges where appropriate.
Press Gazette understands that WENN will also be doing this retrospectively for any Plixi photos used in the past without permission.
Beiny said: "Everyone has turned a blind eye to the use of these pictures up until now, but sooner or later the people who own them are going to say you can't just steal out pictures and republish them without paying for them."
Plixi has been used by a number of celebrities to post candid photos of themselves online.
In September last year actress Demi Moore used a similar service, called Twitpic, to post photos of herself posing in a bikini in front of a mirror to Twitter which were widely published in magazines and newspapers.
Under the terms of service which Plixi users sign up to, the US-based website states: "Plixi does not claim ownership of content you submit or make available for inclusion on the service. However, with respect to content you submit or make available for inclusion on publicly accessible areas of the service, you grant Plixi the following worldwide, royalty-free and non-exclusive license(s), as applicable:
"With respect to content you submit or make available for inclusion on publicly accessible areas of Plixi, the license (with the right to sublicense) to use, distribute, reproduce, modify, adapt, publicly perform and publicly display such content, whether on the service, or through other media.
"This license exists only for as long as you elect to continue to include such content on the service and will terminate at the time you remove or Plixi removes such content from the service; provided, however, that if Plixi distributes or authorizes distribution of any content prior to your removal thereof from the service, Plixi's (and it's sublicenses') rights with respect to such content shall be in perpetuity."