Dependencies: i3-wm, bash, xrandr, curl, feh, imagemagick (convert), python & python-requests

i3-config

# random wallpaper
set $random-wall-cmd /bin/sh $HOME/.config/i3/wallpaper.sh
exec --no-startup-id $random-wall-cmd
bindsym $mod+b exec --no-startup-id $random-wall-cmd

wallheaven.py

#!/usr/bin/env python

import requests
import lxml.html
import sys

url = 'http://alpha.wallhaven.cc/search'


def search(**params):
    page = requests.get(url, params=params, headers={'X-Requested-With': 'XMLHttpRequest'})
    html = lxml.html.fromstring(page.content)
    links = html.xpath('//a[@class="preview"]/@href')
    links = (l.rsplit('/', 1)[1] for l in links)
    return ('http://wallpapers.wallhaven.cc/wallpapers/full/wallhaven-%s.jpg' % l for l in links)


if __name__ == '__main__':
    print(next(search(
        q=sys.argv[1],
        resolutions=sys.argv[2],
        page=1,
        purity=100,
        categories=100,
        sorting='random')))

wallpaper.sh

#!/bin/bash

set -o pipefail

SCRIPT=$(readlink -f "$0")
SCRIPTPATH=$(dirname "$SCRIPT")

# extract resolution of first output (you might simply hardcode that)
RESOLUTION=$(xrandr | grep \* | cut -d' ' -f4 | head -1)

# set the wallpaper from the piped image 
function wallpaper() {
	feh --bg-fill -
}

# generate an image with a centered message and wallpaper it
#         ↓ message     ↓ point size
# message "hello world" 200
function message() {
	convert -background black -fill white \
		-font dejavu-sans-condensed -pointsize $2 \
		-gravity center -size $RESOLUTION \
		caption:"$1" png:- | wallpaper
}

message "Please wait…" 200

( curl -s $($SCRIPTPATH/wallheaven.py '"nature"' $RESOLUTION) | wallpaper ) || message "Something failed." 150