"exiftool gives you great flexibility in how you invoke it.
Depending on which options you are using, exiftool either updates
the supplied image files or works more as a filter: reading images
from your nominated locations and writing them to standard output
or a target directory. When exiftool is operating in filter mode,
you supply the file or directory name you would like to use as the
source as the final argument. You can also use a hyphen to have
exiftool read its data from standard input. In filter mode the
results are written to standard output, or you can use the -w
option to write output images to files instead.
"A typical invocation of exiftool takes an input image, performs
some metadata operations on it, and writes the output to standard
output (filter mode) or back to the original file name, keeping a
backup of the original content as file.jpg_original (update mode).
If you have good backups and you are confident that exiftool works
as expected, you can also update an image without creating backup
files by using the -overwrite_original option."