Nikon Df - Manual (Page 221)

201
I
Protecting Photographs from
Deletion
In full-frame, zoom, thumbnail, and calendar playback, the L
(U) button can be used to protect photographs from accidental
deletion. Protected files can not be deleted using the O button or
the Delete option in the playback menu. Note that protected
images will be deleted when the memory card is formatted (0 22,
272).
To protect a photograph:
1
Select an image.
Display the image in full-frame playback or playback zoom or
highlight it in the thumbnail list in thumbnail or calendar
playback.
Full-frame playback Thumbnail playback Calendar playback