Install Demo application icon in standard location
The icon is curently installed as /usr/share/icons/org.freedesktop.libfprint.Demo.png
The appropriate location would be below /usr/share/icons/hicolor//apps/, see https://specifications.freedesktop.org/icon-theme-spec/icon-theme-spec-latest.html
Currently, the icon has size 196x196, but as there is a sufficient blank area at the borders it is trivial to crop the icon to a standard size of 192x192.