How to change the image label using a script?

Heres what I have now but it would not load/show.

FirstImage = "http://www.roblox.com/asset?id=3960418540" -- Put ID here
SecondImage = "http://www.roblox.com/asset?id=3960438999" -- Put ID here
ThirdImage = "http://www.roblox.com/asset?id=3960454413"


while true do
script.Parent.Image = FirstImage

wait(4)

script.Parent.Image = SecondImage

wait(4)

script.Parent.Image = ThirdImage

wait(4)

script.Parent.Image = FirstImage

wait(4)

script.Parent.Image = SecondImage

wait(4)

script.Parent.Image = ThirdImage




end

Any help?