Set picture to 4 UI Image grid

The easy solution would be to slice up the image in import settings. Then you could easily set each individual image.

To do this dynamically its a bit more complicated, especially since the UI image has a RectTransform but it can be done with some coding. You would need to create a script that does something like this:

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public class Gem : MonoBehaviour
 {
     public List<Image> uiImages = new List<Image>();
     public Texture2D image;
     public int rows = 2;
     public int columns = 2;
 
     // Use this for initialization
     void Start ()
     {
         if ((image != null) && (rows * columns) == uiImages.Count)
         {
             // first verify all GameObjects have been assigned
             for (int i = 0; i < uiImages.Count; i++)
                 if (uiImages[i] == null)
                     return;
         }
     }
 
     public void AssignImages()
     {
         for (int i = 0; i < rows; i++)
         {
             for (int j = 0; j < columns; j++)
             {
                 // you will need to create a sprite based on the portion of the image that you wan to copy
                 // and then assign it to the appropriate image in your list
             }
         }
     }
 }