In order for the player to display the image and occupy the entire screen, the uploaded images will need to be in Full HD 1920×1080 or according to your TV’s resolution requirements.
If you have already uploaded images with a resolution lower than the recommended one, you will see black bars on the sides of the screen.
For more information, please click the link below.
https://www.yodeck.com/docs/user-manual/images-on-screen/#Supported_Resolution