Just load standard library dired-x.el, customize option dired-guess-shell-alist-user, and use ! in Dired, to open whatever program you want, by default on the marked files or a single file, for whatever image-file extensions you want.
C-x v dired-guess-shell-alist-user:
dired-guess-shell-alist-user is a variable defined in dired-x.el.
Its value is nil
You need to provide a path: [[./KLOCKA6.JPG]], otherwise the link is not recognized as a file link. Alternatively, you can make sure that it is recognized as a file link if you write it explicitly as [[file:KLOCKA6.JPG]]. See External links.