This script downloads a new image from Unsplash. It checks whether the screen was locked every 5 minutes. In case of no Internet, it retries every 1 minute and displays the previous picture untill a new one is downloaded.

Dependencies

PHP - Available in repositories of most popular distribution.
Composer - Available in repositories of most popular distribution.
Imagemagick - Specifically, the convert command.
i3lock-color - Available in AUR (For Arch users). Fork of i3lock with more features. Do not use i3lock since this program utilizes the features of i3lock-color.
bash - Most probably will be installed already.