to change timestamps for pictures (in exif), do:

 exiv2 -a '6' adjust *.JPG *.jpg

advances for 6 hours, to update the timestamp of the file do:

 exiv2 -T rename *.JPG *.jpg
Don Okt 19 15:24:27 CEST 2017
anybrowser.gif elektra.jpg fsfe-logo.png patent_button.gif valid-css.png valid-html401.png vim.gif