how first person controller can walk by touching a gui texture of arrow not by keyboard key

var arrowTex:Texture;
static var forwardmovement:int;

function OnGUI(){
    if(GUI.Button(Rect(0,0,25,25), arrowTex){
       forwardmovement = 1.0;
   }
}

Then just change the Character Controller to fit this script.
ie.:
Where the Input is taken(GetAxis), change that var to equal forwardmovement.