How can I resize an image with drag-and-drop?

well , on handed resizing cause you resizing something with one hand(in smart phone you can do scaling with two fingers, well should a must say 1 finger resizing, lol, i meshed up)/ by clicking if on pc.

why you cant resize the image?

  // this resizing your btn in btndown
  yourtBtn.gameObject.transform.localScale *= 0.75f;

Resize the game object that on it, all in hierarchy is Gameobject.

To detect 2dRay form touch(if pc by clicking) do like this :

  //ONupdate
  Ray ray = new Ray();
  RaycastHit hit;
  ray = Camera.main.ScreenPointToRay(Input.mousePosition);
  if (Physics.Raycast(ray, out hit))
  {
       if(hit == yourimage that have collider)
       {
            //do something  
       }
  }

do something like tht.

to get first pos you can do it on btndown, your btn down must be have parameter like "PointerEventData eventData", eventData have position, you can use it. onDrag will have too.