How to show image in full screen with escape button to go back.

@username

Make couroutine and call in start as in the script and check for escape button pressed and do what you want to do.

 class EscapeButtonHandling:MonoBehaviour
 {
 
     private void Start()
     {
         StartCoroutine(UpdateCouroutine());
     }
 
     IEnumerator UpdateCouroutine()
     {
 
         while (true)
         {
 
             if (Input.GetKeyDown(KeyCode.Escape))
             {
                  // Do whatEver You want to do
             }
 
             yield return new WaitForEndOfFrame();
         }
 
     }