How to update movie posters

[Betelgeuse]

I have a problem with some of my movies showing wrong poster. I have updated the poster on the server but can not find a way to correct it using Mediabrowser.
I have tried the "rescan video metadata" button in Serviio console, but it seems to do nothing. (What is it supposed to do?).
I have metadata set to "XBMC .nfo files" because I use Media Companion to create nfo, posters and fanart.

[zip]

It's probably due to the browser's cache. It will either expire in a few days itself, or force removal of the browser's cache files.

I also have this problem. The server has associated adult/pornographic movies/images with some home movies from my camera, and now the server is effectively littered with porn, and the names of some pornographic movies. This is poor, since the kids use it to watch our movies and I have had to unplug it.
I guess that some nefarious sorts upload this content to match with random movie name handles (typically of a phone or handycam filename format) in order to promote their material - free advertising.
Which online metadata service is the safest? I have changed to "MyMovies" since this seems to be a Microsoft service, but the disgusting images persist even after a rescan.
How can I rid my server of this material, or otherwise override the incorrect associations which do appear on other titles: eg. the movie BMX Bandits has been associated with some of my "BMX" titles home videos of BMX riding.
As someone mentioned in another thread, granular control over the associations would be excellent. Opt-in manual approval of associations would also be good, so as to prevent nasty surprises.
Thanks