Please, don't encourage these people to create some restricted site-specific custom app.

Here is John's Background Switcher:

https://itunes.apple.com/gb/app/johns-background-switcher/id...

I use it on Windows and it's very nice, and highly customizable. It works with a lot of sites, and custom searches.

1. Download wallpapers 2. Open Desktop & Screen Saver settings 3. Click the + icon and add the folder the wallpapers were saved to 4. Check "Change picture: Every day"

Mac os app is in development, so don't forget to check it soon)