Nautilus was not generating thumbnails for some
xpm files I had, so I tried to investigate who was responsible for generating thumbnails for xpm files (if any), or any image for that matter. And I stumbled into a wall of misinformation, obsolete specs and frustrated searches.
So, where is the thumbnailer for such "basic" images defined? I've checked
/usr/share/thumbnailers and it only mentions pdf, exe, and video files. No mention of png, jpg bmp, etc. Where are thumbnails of images defined? Wat are the official references about it?