This is "Kanagawa Oki nami ura" from Hokusai Katsushika's "Fugaku Sanjurokkei" (Thirty-six Views of Mt. Fuji).
Both iPhone and Galaxy cases are available. This image is a vertically cropped version of Mt. Fuji and dynamic waves. A horizontal cropped version with almost all the figures is also available, although not all of them due to the aspect ratio of the case itself.