How do I make this image change to the avatar of the name put into the textbox by the player?

I would like to know how to make this surface GUI image label change to the avatar of the name that is put into the textbox on a screengui by a player in-game. I am leaving out all the variables to make it easier to read.

Script:

game.Players.PlayerAdded:Connect(function(main)
	box1avatar.Image = "http://www.roblox.com/Thumbs/Avatar.ashx?x=150&y=200&Format=Png&username=" .. game.StarterGui.announcementholder.Frame.name
end)