This is Debian bug https://bugs.debian.org/783254 reported by Lars Stoltenow.
His steps to reproduce:
convert -size 32770x100 xc:white test.png
feh --fullscreen test.png
Apparently the latest version of imagemagick does no longer allow users to create images that exceed a certain limit but it should be possible to create such images with other means. He also provided a way to fix/work around it
Here is the full bug report:
rendering an imlib image to a X11 window while simultaneously scaling it, causes
a crash when the image width is > 32768 (or 32767 or so).
The bug originally appeared when using feh to view a wide PNG image in
fullscreen (causing it to be downsampled while rendering).
The (apparent) cause of the crash is the __imlib_CalcXPoints calculating
offsets (into image data I think) incorrectly. For not-so-wide images, all
offsets are positive, which makes sense. For wider images, all but the first
offsets are negative, which subsequently causes out-of-bounds memory accesses
and a crash.
I guess this is because the calculations happen with int = 32 bit (even on
amd64). Several intermediate calculations shift left by 16 -> sign bit flips
for > 32768 -> calculated offset becomes negative. (The resulting value is
right shifted by 16 later again, but then of course it is still negative).
A first quick fix that doesn't appear to completely fall apart is attached.
It appears to fix the problem, however I am not sure if there are other parts
that should also use 64 bit numbers.