How do i get screenshots for apple submission?

Yes.

I made a screenshot tool to tackle the issue. Here's a script that, if attached to your main camera, let you grab a screenshot at any resolution you want. Here's how it works:

If set at "2", the "resolution$$anonymous$$odifier" parameter will grab a screenshot at twice the resolution you have in the editor. Ex: Retina is 2048x1536, so set your editor as 1024x768 and grab your screen with a modifier of 2 and you are all set.

To grab a screenshot, press play and press "P" or any other button you have set in "$$anonymous$$eyToPress".

The screenshot will go into a folder called "Screenshot" next to the asset folder of your project.

 using UnityEngine;
 using System.Collections;
 using System;
 
 public class prbScreenshot : $$anonymous$$onoBehaviour {
 
     public string keyToPress = "p";
     public int resolution$$anonymous$$odifier = 1;
     public string prefix = "ss";
     int id;
     bool take = false;
 
     void Start () 
     {
         if (!System.IO.Directory.Exists(Application.dataPath + "/../Screenshots"))
             System.IO.Directory.CreateDirectory (Application.dataPath + "/../Screenshots");
     }
 
     void Update ()
     {
         if (Input.Get$$anonymous$$eyUp (keyToPress)) 
         {
             take = true;
       
         }
     }
     
 
     void OnPostRender () {
 
         if (take) 
         {
             string dateTime =     DateTime.Now.$$anonymous$$onth.ToString()+ "-" + 
                 DateTime.Now.Day.ToString() + "_" + 
                     DateTime.Now.Hour.ToString() + "-" + 
                     DateTime.Now.$$anonymous$$inute.ToString() + "-" + 
                     DateTime.Now.Second.ToString();
             string filename = prefix + id.ToString() + "_" + dateTime + ".png";
             Application.CaptureScreenshot((Application.dataPath + "/../Screenshots/" + filename), resolution$$anonymous$$odifier);
             id++;
             take = false;
         }
     }
 }

@alexandre.fiset that code was pretty useful, you should submit it as an answer. I just changed OnPostRender to a custom function called TakeScreenshot() and called it after take=true in Update().