> I am coming to the conclusion that there is no
> difference between "Update" and "Continue" options.
> Both options seem to overwrite my existing jpg files
> and create new ones.

Update downloads any changed html files and any changed or new jpgs.
Continue uses the already downloaded html files and downloads any changed or
new jpgs.

Because of a bug in versions after 3.32 including the beta 13 the check for
file changed is currently broken and it redownloads everything.