Background image setting and smilies

[MiMi]

Hello, I'm new here and started to custormize a new guestbook.
now I have 2 questions:

The first one - I filled the full url to a background image on my website
into the box of "Background image" in "Design and Layout" section,
but it doesn't appear...why?
Is there any limit to image sizes (max-minimum) or websites to upload background images?

The second one - Is it possible to change or add smilies? If possible, I personally want "waving-hand(welcoming or saying bye)" "hug" "sing" and "king"smilies.
MiMi