Nikon D6 Reference Manual page 799

3
Save changes.
Press J to complete the operation.
D
Hidden Pictures
•
Hidden pictures will be deleted when the memory card is formatted.
•
Revealing a protected image will also remove protection from the
image.
A
Revealing All Hidden Pictures
To reveal all pictures hidden using [Hide image], choose [Deselect all] in
the [Hide image] display.
D The Playback Menu: Managing Images 747