--

Reproducing this state may be a little bit tricky, anyway evaluate the
following lines, starting with `emacs -Q'.

(defvar img "foo.png");; The image should be taller then the window
                      ;; it's displayed in.
(setq debug-on-error t)
(find-file img)
(redisplay t)         ;; If in batch mode.
(image-scroll-up 999)
;; The image should be scrolled to the bottom now, while point equals 1.
(posn-at-point (point-max) (selected-window))

--

Note, that this bug may make switching buffers difficult in certain
situations, as was reported here:
https://github.com/politza/pdf-tools/issues/200

-ap