https://www.theverge.com/circuitbreaker/2017/10/13/16468730/pixel-photo-storage-google-photos-workaround

Developers have found a way to pirate cloud storage from Google Photos. Google offers unlimited storage of full-resolution photos and videos for its Pixel users, and now, some developers have found a way to subvert that Pixel device requirement to obtain plentiful Google Photos storage on any Android device running Nougat or higher.

The workaround isn't simple. Users will have to root their device, download a file that's already found on Pixel phones, load that file onto their device, and in some cases, go even further with additional, more complicated adjustments. You can view the full hack here on XDA Developers. A developer initially created the workaround to obtain exclusive Pixel wallpapers and seemed to view unlimited Google Photos storage as an added bonus.