صورة:Stamp Tanganyika 1925 10c.jpg

This is because it is one of the following:

1. It is a photograph created by the United Kingdom Government and taken prior to 1 June 1957; or
2. It is a photograph or an engraving created by the United Kingdom Government and commercially published prior to 1958; or
3. It is an artistic work other than a photograph or engraving (e.g. a painting) which was created by the United Kingdom Government prior to 1958.

More information. See also Copyright, Crown copyright artistic works and HMSO Email Reply.