Change Login background with custom image in ElementaryOS 7.1

changeBG.sh

#!/bin/bash

# Resources
# https://github.com/Blackmanx/elementaryOS-lockscreen-bgreplacer

if [ $(id -u) != 0 ];then
    echo -e "Error: Run script as root user"
    exit 1
fi

if [ -z "$1" ];then
    echo -e "Error: Missing path image\n\n=> Usage: ./bg.sh /home/user/wallpaper.png\n"
    exit 1
fi

if [ "$1" == "--reset" ];then
    apt install -y --reinstall io.elementary.greeter
    echo -e "\n=> SUCCESS: Background reset OK"
    exit 0
fi

BG_IMAGE="$1"

if [ ! -f "$BG_IMAGE" ];then
    echo -e "Error: File not found\n"
    exit 1
else
    echo "================== Start BG =================="
fi

dependencies_meson(){
    apt install -y valac libaccountsservice-dev libgtk-3-dev libgranite-dev libhandy-1-dev liblightdm-gobject-1-dev libmutter-10-dev &> /dev/null
}

install_ninja(){
    #python3 -m pip install ninja
    if [ $(which ninja) ];then
        echo "=> Ninja found : $(ninja --version)"
    else
        echo "=> Ninja not found (installing...)"
        apt install -y ninja-build
    fi
}

install_meson(){
    if [ $(which meson) ];then
        echo "=> Meson found : $(meson --version)"
    else
        echo "=> Meson not found (installing...)"
        if [ ! $(which pip) ];then
            apt install -y python3-pip &> /dev/null
        fi
        python3 -m pip install meson
    fi
}

config_greeter(){

    echo "=> Config greeter"
    if [[ -d /tmp/greeter ]]; then
	    rm -rf /tmp/greeter
    fi

    # Download and configure greeter
    git clone https://github.com/elementary/greeter.git /tmp/greeter &> /dev/null

    rm -rf /tmp/greeter/data/texture.png
    cp $BG_IMAGE /tmp/greeter/data/texture.png

    # Replace path to new texture's path.
    sed -i "s/resource\:\/\/\/io\/elementary\/desktop\/gala\/texture\.png/resource\:\/\/\/io\/elementary\/greeter\/texture\.png/" /tmp/greeter/compositor/SystemBackground.vala
}


build_greeter(){
    config_greeter

    echo "=> Build greeter"
    cd /tmp/greeter
    meson _build --prefix=/usr > /dev/null && ninja install -C _build > /dev/null

    if [ $? != 0 ];then
        echo -e "\n=> ERROR: Failed to build"
    else
        echo -e "\n=> SUCCESS: Background updated OK"
    fi
}

install_ninja
install_meson
dependencies_meson

build_greeter