The postcards date back almost 100 years

The images were found on SMS Karlsruhe by a diver who alerted Historic Scotland to his discovery.

It has appealed for collectors to help shed light on their background as experts work on conserving the images.

The cruiser was one of seven German vessels scuttled in Scapa Flow in 1919, now designated as ancient monuments.

This has given them full legal protection while allowing divers to visit the wrecks without a special licence.

Historic Scotland said the postcards and photographs were spotted by a diver last year.

Tin boxes

Some were recovered in October last year to establish whether they could be conserved.

When that operation proved a success local firm SULA Diving was brought in to retrieve the remaining images.

Bobby Forbes of SULA said: "The postcards had been kept in tin boxes which have gradually eroded, explaining why they have lasted so long under water.

A conservative estimate would be 100 to 200 cards Deirdre Cameron Historic Scotland

"The corrosion from the boxes welded the stacks together and it was a very delicate operation to separate them."

Deirdre Cameron, an inspector of ancient monuments with Historic Scotland, is in charge of the project.

She said the 15 stacks of paper would now be separated and conserved.

"Once this is done the images will be clearer and should be easier to identify," she said.

"We will also know just how many items we are dealing with. A conservative estimate would be 100 to 200 cards."