On June 15th, 2018 500px shut off their API. Photo Paper's features rely on the 500px API and no longer function without access to the API.
I'm a big fan of 500px, from time to time I post my photos there and I'll happily spend hours looking through the amazing photos that others have posted. One day I was staring at the same boring wallpaper on my phone and I thought it would be really nice to have a live wallpaper that used photos from 500px. Unsurprisingly there are several in the Play Store ranging from really bad to pretty good. I gave them a try, but I wasn't very happy with them. Several of them are freemium and most of the ones I've tried are live wallpapers and continuously use a lot of ram. It also bugged me that none of them were open source.
After thinking about if for a little while, I decided to develop my own app that automatically updates the wallpaper instead of being a live wallpaper. Using a few libraries it was very easy to develop in just a few hours time. Users of the app have a range of options for filtering the type of photos they would like to see as their wallpaper along with how frequently they should update. I've released Photo Paper to the Play Store and it is also open source on GitHub.