Toggle input with sprite swap instead of checkmark?

here another version, use toggle as usual, but with this component attached the background is disabled/hidden, when checkmark is shown:

 using UnityEngine;
 
 namespace UnityEngine.UI
 {
     [ExecuteInEditMode]
     public class ToggleGraphicSwap : MonoBehaviour {
 
         Toggle _toggle;
         Toggle toggle {
             get { return _toggle ?? (_toggle = GetComponent<Toggle>()); }
         }
 
         void Awake() {
             toggle.onValueChanged.AddListener(OnTargetToggleValueChanged);
         }
 
         void OnEnable() {
             toggle.targetGraphic.enabled = !toggle.isOn;
         }
 
         void OnTargetToggleValueChanged(bool on) {
             toggle.targetGraphic.enabled = !on;
         }
     }
 }

I ended up using this

 using UnityEngine;
 using System.Collections;
 using UnityEngine.UI;
 
 public class ToggleSpriteSwap : MonoBehaviour {
 
     public Toggle targetToggle;
     public Sprite selectedSprite;
 
     // Use this for initialization
     void Start () {
         targetToggle.toggleTransition = Toggle.ToggleTransition.None; 
         targetToggle.onValueChanged.AddListener(OnTargetToggleValueChanged);
     }
 
     void OnTargetToggleValueChanged(bool newValue) {
         Image targetImage = targetToggle.targetGraphic as Image;
         if (targetImage != null) {
             if (newValue) {
                 targetImage.overrideSprite = selectedSprite;
             } else {
                 targetImage.overrideSprite = null;
             }
         }
     }
 }
 

where do you attach this? I cant seem to see anything change. I have put it onto my canvas, linked the toggle and sprite, but nothing happens

put this code after line 20 and line 22.

 if (newValue) {
     targetImage.overrideSprite = selectedSprite;
     targetImage.enabled = false;
 } else {
     targetImage.overrideSprite = null;
     targetImage.enabled = true;
 }

When toggle on, Checkmark will show, and targetImage(Background) hide. Toggle off, Checkmark will hide, and targetImage(BG) will show.