How to include internal thubnails in .nfo

Good day! I'm trying to write my own paser of mp4 tags in video file to construct metadata in .nfo format. This is example of such file:
But thubnails did not pass to dlna "client" xbmc from serviio server. Is it wrong to write tag:
<thumb>masaki.jpg</thumb>
with a file placed in the same directory. Should I use hyperlink only in "tumb" tag or it is possible to point out local file? Or the tag "thumb" is simply ignored by Serviio?
- Code:
<movie>
<title>Masaki</title>
<genre>Animation</genre>
<year>2008</year>
<thumb>masaki.jpg</thumb>
<fileinfo>
<streamdetails>
<video>
<codec>h264</codec>
<aspect>2.35</aspect>
<width>1920</width>
<height>816</height>
</video>
<audio>
<codec>ac3</codec>
<language>eng</language>
<channels>6</channels>
</audio>
<audio>
<codec>ac3</codec>
<language>jap</language>
<channels>2</channels>
</audio>
<subtitle>
<language>spa</language>
</subtitle>
</streamdetails>
</fileinfo>
<actor>
<name>Masaki</name>
<role>Himself</role>
</actor>
</movie>
But thubnails did not pass to dlna "client" xbmc from serviio server. Is it wrong to write tag:
<thumb>masaki.jpg</thumb>
with a file placed in the same directory. Should I use hyperlink only in "tumb" tag or it is possible to point out local file? Or the tag "thumb" is simply ignored by Serviio?