image-mode buffers are scrolled down without user intervention sometimes
when another buffer content is updated.  I can reliably reproduce this
using eww.  To demonstrate,

    1. emacs -Q
    2. Visit attached image file.
    3. s o ;; to make the window show only some part of the image
    4. M->
    5. C-x 3 ;; split the frame into two windows
    6. M-s M-w search for something here RET
    7. C-x o ;; switch to the image-mode buffer
    8. Observe image-mode buffer moving to the beginning of image when
       the eww buffer gets updated with the webpage content.

(7,8) You have to be quick enough to switch back to the image-mode
buffer as otherwise, this behaviour is not seen.

By (2), I mean to say that the image should be large enough such that
only a part of the image is shown in the window, unlike what is seen
when you visit the file initially.

This does not happen only with eww but in other scenarios as well.  But
I am unable to reproduce this behaviour in those scenarios as they are a
lot more involved.