It should be possible to have one or more decoy passwords. Under pressure the journalist reveals a decoy password. When entered, the camera presents the view of an SD card with various information that is okay to reveal to the authorities. The real information protected by a different password is still protected.

The implementation of 'real' and 'decoy' passwords should be identical. The decoy isn't implemented any differently than the real. Watching the camera go through the motions to access the file system through that password should not reveal whether that password is real, because the 'real' password isn't any different than a decoy password used to access decoy files on the SD card.

Under more pressure, the journalist could reveal that the password previously given was in fact a decoy, and now the journalist will give the 'real' password -- but it may be a decoy as well. There is no way to tell.