Mizuu automatically fetches a random backdrop image when you view movie details, but you can actually choose one yourself that’ll be downloaded locally to your device. Fortunately, it’s really easy to do!
To access the backdrop browser, simply tap on the backdrop image itself. A backdrop browser will appear and once you find a cool backdrop, just press it and hit “OK” to the download dialog. Mizuu will then download the backdrop cover, and use it every time you view the movie or TV show in question.
Alternatively, you can press the Menu button and select the Change backdrop option from the menu.