I mean the gray border around thumbnails in icon view.
thumbnail_frame.png is not present in
/usr/share/pixmaps/, not even a nautilus folder.
I have Ubuntu Gnome 17.04.
This is far from a good solution, but its the best I have found so far. Because the feature this uses is apparently supposed to only be for speeding up development, I would hope that there is a better way. But I haven't found anything else that works for me. (in Nautilus 3.20.4)
Based on https://developer.gnome.org/gio/stable/GResource.html , you can specify 'overlay' resourse directories which replace the default resources with the
G_RESOURCE_OVERLAYS environment variable. With this you could provide a replacement thumbnail_frame.png that is completely transparent, effectively removing it.
SOME_ABSOLUTE_PATH could be something like
/home/cristian/replacementIcons but that's up to you.
SOME_ABSOLUTE_PATH/thumbnail_frame.png as a 512x512 transparent image. (I'm not sure if the size matters, but that's what I tested.)
Then you can launch nautilus from the terminal with
In order to be able to make this work with opening nautilus from anywhere, you can edit /etc/environment as root and add
G_RESOURCE_OVERLAYS="/org/gnome/nautilus/icons=SOME_ABSOLUTE_PATH/icons" at the end of the file.
Then reboot and the thumbnail frames should have disappeared.