Digital Photo Cameras use the Exif metadata standard to store image metinformation (geotag, image properties, timestamp) in the (JPG, TIFF) image.
> identify -verbose IMG_8148.JPG | grep DateTimeOriginal exif:DateTimeOriginal: 2015:11:09 17:18:55
# example exiftool "-FileName<CreateDate" -d "%Y%m%d_%H%M%S.%%e" DIR # keep original filename: exiftool '-FileName<CreateDate' -d d%Y%m%d-%H%M%S-%%f.%%e DIR