This is a quick and dirty solution for an unanimated custom splash screen during boot.

First of all, you need to install fbi:

apt-get install fbi

Copy your custom splash image to /etc/ and name it "splash.png".

Next, create an init.d script called "asplashscreen" in "/etc/init.d/".

I chose "asplashscreen" with an "a" at the beginning to be sure it starts first.

#! /bin/sh
### BEGIN INIT INFO
# Provides:          asplashscreen
# Required-Start:
# Required-Stop:
# Should-Start:      
# Default-Start:     S
# Default-Stop:
# Short-Description: Show custom splashscreen
# Description:       Show custom splashscreen
### END INIT INFO


do_start () {

    /usr/bin/fbi -T 1 -noverbose -a /etc/splash.png    
    exit 0
}

case "$1" in
  start|"")
    do_start
    ;;
  restart|reload|force-reload)
    echo "Error: argument '$1' not supported" >&2
    exit 3
    ;;
  stop)
    # No-op
    ;;
  status)
    exit 0
    ;;
  *)
    echo "Usage: asplashscreen [start|stop]" >&2
    exit 3
    ;;
esac

:

Then make that script executable and install it for init mode rcS:

chmod a+x /etc/init.d/asplashscreen

insserv /etc/init.d/asplashscreen

Reboot and watch your custom splash screen:

reboot