I have an older PB360 not a newer PB360+. If it still works the same, it is necessary to put your personal images in a specific named directory in internal memory, namely [root:]
\system\logo The images need to be in .bmp format and in greyscale (4BPP I think).
You change the image using the options
Main menu - Settings - Appearance followed by
Boot logo or
Power-off logo
It this info is outdated then perhaps someone with a PB360+ will be along shortly with better info