Changing the time on several dozen jpegs at once

[Dotan Cohen]

A friend had let my camera sit overnight with no batteries, and when
he finally relaced them he set the clock to AM time instead of PM
time. How can I add 12 hours exactly to all the photos in a certain
directory? I would prefer a solution that would not lose jpeg image
quality, as I know that rewriting a jpeg reduces quality in most
cases. The windows program JpegHammer does this, but I'd rather not go
hunting for a windows computer ever time I get stuck. Even a cli
command (or script) would be most helpful. Thanks in advance.

Dotan Cohen
http://gmail-com.com