Setting picture dates?

["Derek Vandivere" <derek vandivere net>]

Is there any way to update the date and time stamp on pictures? I've
got a bunch of scanned in pics for which I know the precise date, but
can't see any way to set them. I guess adding / editing EXIF tags
would do the trick, but it seems that the data must be stored
somewhere, since it takes the date of import rather than the create or
modify date...

And is any help needed in terms of documentation or whatever? I'm not
the world's best coder, but it'd be nice to help out with something.

Cheers,
dersk