Dunno, but I got pictures working by putting them in [userstore]/images/ and using Collections Manager to unhide the Images collection at the very end of the collections list.
Works directly in KindleOS.
There might be a way to show them through KUAL, I do know that Aeris'
Native Menu includes a Gallery for viewing contents of said folder.
I'm afraid I don't have a clue about Duokan, I won't touch the thing.