XnView Software

Just uncheck in Tools | Settings | Database the "Use thumbnail caching"

Thank you very much, indeed.

@RMMM
there's a file called ~/.xnviewmp/Thumb.db containing all those thumbnails. You can delete that file by hand from time to time, however, it will be recreated on every restart of XnViewMP. If you wish you can do that in an automated way by writing a small script:

#!/bin/bash
# ~/bin/cleanup.sh ...