Add files manually with Thumbnail URL in Mysql database

Hello,

I want to add file in Kodi manually with mysql.
Everything work : Title, Summary, Url from the file on Internet.
But I can not add pictures for these files.

In Mysql>MyVideos>episode I insert the thumb tag with the url of the image in c06. 
It is the same code of another file that works but no image appears that I select the file.
<thumb>http://thetvdb.com/banners/episodes/269642/4705391.jpg</thumb>

Can you help me ?

Thank you