Nikon D3300 - Manual (Page 204)

184 Playback and Deletion
In full-frame, zoom, thumbnail, and calendar playback, the
A (L) 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 (
0 234).
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.
2
Press the A (L) button.
The photograph will be marked with a P icon.
Protecting Photographs from Deletion
Full-frame playback Thumbnail playback
A (L) button