If you're working on this assignment and you can't find the ImageFX script that's mentioned around 4:45, you can do the following:
Alternatively, you can simply paste the following into a new script:
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
public class ImageFX : MonoBehaviour {
public Material mat;
void OnRenderImage(RenderTexture source, RenderTexture destination)
{
Graphics.Blit (source, destination, mat);
}
}