I just did this command in c:/Users/A_USER_NAME/
robocopy . g:\Pictures\. /Z /XO /S /LOG:./robocopy_log.txt
where
/Z is copy files in restartable mode.
/XO eXclude Older files and X+Alpha(O) as in old.
this only copies file to destination if it is newer
then target file.
/S is copy Subdirectories, but not empty ones.