When you request a screenshot, an extra column will appear “Thumbnail”. If it doesn’t you can enable it by selecting it from the list of columns you have enabled in the grid.
XMR is pre-installed with Docker yes. The only thing you need to set is the XMR public address on the Settings page of the CMS.
It should be
cms.example.org is the fully qualified hostname of your server where Xibo is installed. You can use an IP address instead if you want.
If XMR is working properly with your Players, then you’ll get a new screenshot in the Thumbnail column in 1-10 seconds time if the Player is online.
If XMR isn’t working, it should return a screenshot next time it collects - however there are bugs with that behaviour in older Players, so you may never get a screenshot returned. In that case, make sure you have your Players upgraded to the latest versions.