The background was an area of a photograph or footage.
History
The Ninth Doctor and Rose Tyler were visible in the background of a photograph of Charles Dickens in Cardiff 1869. (PROSE: Rose sighting confirmed)
The Ninth Doctor was also visible in some photographs taken of the Manhattan Project, in the background to the right of Oppenheimer. (PROSE: Have You Seen This Man?)
In 1946, the Ninth Doctor was visible in the background of two photographs of a village, near the War memorial. (PROSE: Have You Seen This Man?)
In 1948, the Ninth Doctor, again, was visible in the background of a photograph of Random C's gran in Devon, seemingly talking to a donkey. (PROSE: Have You Seen This Man?)
In the 20th century, the Ninth Doctor was also in the background of a photograph taken of David Grant's father during his "army days". (PROSE: Have You Seen This Man?)
In the 2000s, the Ninth Doctor was visible in the background of footage of the Royal Wedding. (PROSE: Have You Seen This Man?)