In the config file at

~/.config/i3/.i3status.conf

you will find lines that define the function of variety. Variety is a wallpaper changer and will also give you new wallpaper from the standard sources or you can add more personal sources.
More information about variety in this article.

variety -t  is trash the wallpaper
variety -n gives the next wallpaper
variety -p gives the previous wallpaper
variety -f  make it a favorite wallpaper

You can add any program with extra parameters and execute it.

Variety preferences is set to floating.

variety

Another example in this regard is the scrot line.

bindsym Print exec scrot '%Y-%m-%d-%s_screenshot_$wx$h.jpg' -e 'mv $f ~/Pictures/'

A tutorial to show you the code in the config file.