I don't know if it has changed with KSM9 but when you create your "poweroff_info.html" you can use something like mine:
<html>
<head>
<title>kobo menu info</title>
<style type="image/png">
p {
margin-top: 0.5em; }
</style>
</head>
<body>
<img src="/mnt/onboard/.adds/kbmenu/txt/poweroff.png">
</body>
</html>
As you can see I just put my poweroff.png in the txt folder where the poweroff_info.html resides.
By the way, I get this image for my power off in KOReader, as well.
Luck;
Ken