I have read all of the documentation on Ambient Mode (Q90R) that I can find, and have looked through endless community threads, but it looks as though Ambient Mode will not let you set your own picture to fill the whole frame of the TV. As an artist, this is incredibly disappointing as I would like to be able to create my own frames in the image itself, and I cannot display the whole of my art work because the incredibly wide frame crops the top and bottom (yes I have read the documentation on cropping photos for ambient mode too, it doesn't let you display 16:9 content no matter what you do).
I was also very disappointed to find out that almost all of the ambient mode themes I found in articles all over the internet are not available at all. Only the select few that come with the TV are available.
Please don't send me a link to documentation, trust me, I have read it.