Use relative image path in template.

ticdesk_org/templates/ticdesk_org/list_participants.tex

@@ -15,7 +15,7 @@
 \hline\rowfont\bfseries Foto & Nachname & Vorname & Geburts\-datum & Benutzer & Handynummer \\\hline
 \endhead
 {% for person in persons %}
-\parbox[c][3cm]{2.25cm}{\includegraphics[width=2.24cm,height=2.99cm,keepaspectratio=true,valign=c]{ {{ person.uid }} }} & \nohyphens{ {{ person.sn }} } & \nohyphens{ {{ person.given_name }} } & \nohyphens{ {{ person.date_of_birth }} } & \texttt{ {{ person.uid }} } & \nohyphens{ {{ person.mobile }} } \\\hline
+\parbox[c][3cm]{2.25cm}{\includegraphics[width=2.24cm,height=2.99cm,keepaspectratio=true,valign=c]{ {{ person.jpeg_photo__rel }} }} & \nohyphens{ {{ person.sn }} } & \nohyphens{ {{ person.given_name }} } & \nohyphens{ {{ person.date_of_birth }} } & \texttt{ {{ person.uid }} } & \nohyphens{ {{ person.mobile }} } \\\hline
 {% endfor %}
  \end{longtabu}
 \end{document}