I recommend you to use this beautiful lake picture as your screensaver for iPhone 7. An alternative lockscreen with nature photo in high resolution. The resolution of this screensaver also been configured in 750x1334, an official resolution of Apple iPhone 7. I use this picture as the #9 of all 10 screensavers that you can download in free.
Furthermore, here are all complete 10 screensavers that you can select and download: