Image texture not visible when loaded in script, and button placement wrt image

Hello, in the example below, I have made prefabs for the UI Button and Raw Image, as I didn't find a way to create them otherwise by script. In order to run this example, create a minimal example with only a Canvas and attach the script to the Canvas. This script runs without errors, but I still have two problems:

1) the texture of the image (a photograph) does not appear in the editor; but if I create the RawImage in the editor, I can see it; I guess something must be missing?

2) I have some trouble centering the button and currently the button is not centered. How should I do it better in the script?

Many thanks.

 using UnityEngine;
 using UnityEngine.UI;
 
 public class Bug3 : MonoBehaviour
 {
   Canvas canv;
   GameObject prefab_button,prefab_image,play;
 
   public void Start() {
     prefab_button = Resources.Load("Prefabs/Button") as GameObject;
     prefab_image = Resources.Load("Prefabs/RawImage") as GameObject;
     Texture2D raw = Resources.Load<Texture2D>("Images/P1450962.JPG");
     canv = GameObject.Find("Canvas").GetComponent<Canvas>();
 
     // background image
     background=Instantiate(prefab_image,new Vector3(0,0,0),Quaternion.identity);
     background.name="Background";
     background.GetComponent<RectTransform>().SetParent(
                            canv.GetComponent<RectTransform>());
     background.GetComponent<RawImage>().texture=raw;
     background.GetComponent<RectTransform>().position=new Vector3(0,0,0);
     background.GetComponent<RectTransform>().sizeDelta
       =new Vector2(Display.main.systemWidth,Display.main.systemHeight);
     
     // button 1
     play=Instantiate(prefab_button,new Vector3(0,0,0),Quaternion.identity);
     play.name="Play";
     play.GetComponent<RectTransform>().SetParent(
                               background.GetComponent<RectTransform>());
 
     play.GetComponentInChildren<Text>().text = "Play";
     play.GetComponentInChildren<Text>().fontSize=23;
     play.GetComponent<RectTransform>().localScale=new Vector3(1,1,1);
     play.GetComponent<RectTransform>().sizeDelta=new Vector2(200,50);
     play.GetComponent<RectTransform>().position=new Vector3(-100,-10,0);
 
   }
 
 }