Looks like ImageMagick strikes again — except that I can’t reproduce this locally.
Uploading StefanD’s file on meta and try results in a solid black image; uploading it to my local Discourse does not. Since I’m not using the Docker setup, is the ImageMagick version in the docker base image outdated?
Mine is:
Version: ImageMagick 6.9.0-3 Q16 x86_64 2015-01-17 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2015 ImageMagick Studio LLC
Features: DPC Modules OpenMP
Delegates (built-in): bzlib freetype jng jpeg ltdl png tiff zlib