The image, taken last week, shows the King carrying out official government duties in the Eighteenth Century Room at Buckingham Palace.
Red boxes contain papers from government ministers in the UK and the realms, as well as Commonwealth representatives.
Documents are sent from the private secretary’s office to the King, wherever he is around the world, in a locked, red despatch box.
These include papers which require a signature, briefing documents and information about forthcoming meetings.
In the picture, Charles is sitting at a desk. Papers, one tied with a ribbon, are next to him.
A black and white photograph of the late Queen and Duke of Edinburgh is also shown, given to King George VI for Christmas in 1951 by the couple.
Previously, luxury British leather goods company Barrow Hepburn & Gale confirmed that boxes for Charles were in production.
On September 11, a spokesman for the firm said the King would initially receive more than six boxes, which would carry the new royal cypher.
It is possible that 10 to 12 boxes will be made and delivered in phases over the coming months.
Every box, the price of which is never released, has its own coded lock and is designed to last for many years.
The company says on its website that its boxes “follow their holder around the world, ensuring they can execute the responsibilities of their office”.
It adds: “Wherever in the world the sovereign or minister is, the red box is close by.
“Our despatch boxes are not only an elegant design, but are functional and secure.”
In September 2015, the royal family Facebook account said the Queen received red boxes every day of her reign, including weekends, but not on Christmas Day.
The post said the Queen was still using boxes made for her coronation in 1953, which had been “periodically refurbished” to keep them in good condition.
Barrow Hepburn & Gale said the role of the boxes “has not changed for over a century”.
It added: “There are two possible reasons why the despatch box became the iconic red colour.
“The widely-accepted reason relates to Prince Albert, consort to Queen Victoria, who is said to have preferred the colour as it was used prominently in the arms of his family, the Saxe-Coburg-Gotha.
“However, there is a school of thought with origins dating back to the late 16th century, when Queen Elizabeth I’s representative, Francis Throckmorton, presented the Spanish ambassador, Bernardino de Mendoza, with a specially constructed red briefcase filled with black puddings.
“It was seen as an official communication from the Queen, and so the colour red became the official colour of the state.”