Drag and Drop background image maximum size on interactive video

Hi everyone,
I'm working on an interactive video, it's HD720. I'm inserting a Drag and Drop activity, a background image and setting it's size to 1280x720 (image actual size is the same), but when I visualize it the image is too small, I can barely read the informations.
Is there a limit to this background image size? 

Oh, and what is the criteria to position this window on the left or the right side of the screen?

Thanks to you all.