full-screen background image

When you specify a rotation, the image starts getting centered in the middle - so all you need to do is use some of the code used in other watchfaces with Math.sin/cos to change the x and y coordinates. Rotation is in radians not degrees too: https://banglejs.com/reference#l_Graphics_drawImage

Faking flash storage in the emulator is possible, but it's low priority for me right now since there's more work to do to actually make the emulator 'remember'. Right now I'm interested in actually getting the real watch working well ready for next month :)

big image ... Where I can find this in source code?

It should 'just work'. If you write an image into flash memory as an 'image string' (I'm working on some tools to do this nicely in the IDE) then you can just do g.drawImage(require("Storage").read("img")) and it'll do it