For my AuraHD I have the following:
<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>
For my "poweroff_info.html". The
Poweroff.png is 1040x1387 bit depth 32, its 361KB.
Works fine.
The image was created using Gimp2 to fit the full screen.
Luck;
Ken