Nikon D3300 - Manual (Page 270)

250 B The Setup Menu: Camera Setup
A File Names
Photographs are stored as image files with names of the form
“DSC_nnnn.xxx,” where nnnn is a four-digit number between 0001 and
9999 assigned automatically in ascending order by the camera, and
xxx is one of the following three-letter extensions: “NEF” for NEF (RAW)
images, “JPG” for JPEG images, or “MOV” for movies. The NEF and JPEG
files recorded at a setting of NEF (RAW)+JPEG have the same file names
but different extensions. Copies created with image overlay (
0 272)
and movie edit options ( 0 164) have file names beginning with
“DSC_” ; copies created with the other options in the retouch menu
have file names beginning with “CSC” (e.g., “CSC_0001.JPG”). Images
recorded with the Color space option in the shooting menu set to
Adobe RGB (
0 225) have names that begin with an underscore (e.g.,
“_DSC0001.JPG”).