A script that saves the KDE Picture of the Day (POTD) you can set on a cronjob to keep a history of all domains.

savebgs.sh

#!/bin/bash

today=$(date +%Y-%m-%d)
dir=$(realpath ~/Pictures/Daily)
mkdir -p "$dir"

for path in ~/.cache/plasmashell/plasma_engine_potd/*; do
  name=$(basename "$path")
  saved="$dir/$today-$name.png"

  if [ ! -f "$saved" ]; then
    # echo "Copying"
    cp "$path" "$saved"
  fi
done