The director of operations says the company has complied with search warrants under the ECPA about a dozen times since May

The photo-sharing app Snapchat has admitted to handing over to American law enforcement agencies images not yet seen by its users.

In a blogpost on Monday, the company outlined the circumstances under which it has given photos – which the company calls "snaps" – to investigators.

“Since May 2013, about a dozen of the search warrants we’ve received have resulted in us producing unopened snaps to law enforcement,” said Snapchat director of operations Micah Schaffer. The only photos handed over have been unopened snaps, because those are the only images the company stores on its servers.

Snapchat works by allowing users to take photos or short videos, then share them with friends for up to 10 seconds before the image self-destructs. If a recipient screenshots the photo, the app alerts the original sender, though hacks to interrupt this function do exist.

In a blogpost in May, Snapchat said once a photo has been opened by all of its recipients, it is deleted from the servers. A forensic software company said it can recover the deleted photos from Android phones and was working on a way to recover them from iPhones.

The photos must be uploaded on company servers to get to the recipient, and Schaffer said only he and the co-founder Bobby Murphy have access to a tool that lets them manually retrieve unopened snaps.

The company said it would retrieve an unopened snap if it receives a search warrant and the snap is still on its server, under requirements by the federal Electronic Communications Privacy Act (ECPA).

Schaffer said he was clarifying Snapchat’s access policy following the release of the app’s new stories feature, which organizes snaps together. These photos can be viewed repeatedly in the first 24 hours after being sent and are then deleted from the company’s servers. The same legal requirements apply to stories and snaps.

Snapchat is thought be worth about $800m. A former friend of Murphy and Snapchat’s co-founder Evan Spiegel is suing the pair for 20% share into the company.