Input.mousePosition doesnt work

I want to drag an image of a canvas, i'm using the onDrag function to set the position of the image to the position of my mouse but when i run the application, and i try to drag the image, the image dissapear, but i realized that the image doesn't dissapear, but the position of the image is not the same as the mouse, when my mpuse gets the values, for example: (204, 15, 0) the image gets values like: (4676, 2345, 0) and i dont know why. Please help, this is my code.

using UnityEngine; using System.Collections; using UnityEngine.EventSystems;

public class NewBehaviourScript : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler {

 public static GameObject item;
 Vector3 startPosition;

 public void OnBeginDrag(PointerEventData eventData)
 {
     item = gameObject;
     startPosition = transform.position;

     Debug.Log(Input.mousePosition);
 }

 public void OnDrag(PointerEventData eventData)
 {
     transform.position = Input.mousePosition;
     Debug.Log(Input.mousePosition);
 }

 public void OnEndDrag(PointerEventData eventData)
 {
     item = null;
     transform.position = startPosition;
     Debug.Log(Input.mousePosition);
 }

}