This script adds a border to the top or the side, this scripts needs CameraSize.cs

CameraBorder.cs

using UnityEngine;
using System.Collections;

namespace StandardAssets{
  
	/// <summary>
	/// Adds a border to the top or the side.
	/// Add this one to the child camera!
	/// </summary>
	[ExecuteInEditMode]
	public class CameraBorder : MonoBehaviour {
	  /// <summary>
	  /// The border Texture (a 1x1 black dot is enough)
	  /// </summary>
	  public Texture border;
	
	  void OnGUI() {
	
	  	//Ensure were on the top
	  	GUI.depth = 10;
	  	//Not needed, but to be sure
	  	GUI.color = Color.black;
	
	  	if (!CameraSize.letterbox) {
	  		GUI.DrawTexture(new Rect(0, 0, Camera.main.pixelRect.x, GetComponent<Camera>().pixelRect.height), border);
	  		GUI.DrawTexture(new Rect(Camera.main.pixelRect.width + Camera.main.pixelRect.x, 0, GetComponent<Camera>().pixelRect.width - Camera.main.pixelRect.width, GetComponent<Camera>().pixelRect.height), border);
	  	} else {
	  		GUI.DrawTexture(new Rect(0, 0, Camera.main.pixelRect.width,Camera.main.pixelRect.y), border);
	  		GUI.DrawTexture(new Rect(0,Maths.PixelToRect(Camera.main.pixelRect.y), Camera.main.pixelRect.width, Camera.main.pixelRect.y), border);
	  	}
	
	
	  }
	}
}