Error creating public variable from C# script in Unity 3d

I have the following situation. I am trying to place an image from a C# script in Unity 3d, when reading a pattern with Vuforia . What is happening to me is that from the moment I create the public variable for the image, it tells me that it is ambiguous .

In that same scene I have a text that I insert from a database, inside a UI element type text and the image must be above that text. With the text I have no problem. The problem is appearing to me with the image. if I remove UnityEngine.UI the conflict with the image is removed but I can't use the text UI. Now if I remove Vuforia there if I don't have the conflict with the image but reading the pattern doesn't work for me. Below I leave the code to see if you can help me to be able to work with the two elements without sending me the ambiguous message .

Thanks.

Mistake:

error CS0104: Image' is an ambiguous reference between Vuforia.Image' and `UnityEngine.UI.Image'

Code

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

using Vuforia;
using UnityEngine.UI;

using Mono.Data.Sqlite;
using System.Data;
using System;
using System.IO;

public class reproduccionAudio : MonoBehaviour, ITrackableEventHandler


{

 private TrackableBehaviour mTrackableBehaviour;

    //public AudioClip otherClip;
    private AudioSource audio;
    private AudioSource[] allAudioSources;
    public Text textoLibro;
    private SqliteConnection dbconn;
    private SqliteCommand dbcmd;
    private SqliteDataReader reader;
    private string conn;
    private string namedb = "usuario.bytes";
    public int nParrafo;
    public Image imgEscena;

        void Start()
        {
            //Traemos el valor del GameObject y lo acipnamos el audioSouce
            audio = GetComponent<AudioSource>();

            imgEscena = GameObject.Find ("Escenas").GetComponents<Image> ();

            mTrackableBehaviour = GetComponent<TrackableBehaviour>();
            if (mTrackableBehaviour)
            {
                mTrackableBehaviour.RegisterTrackableEventHandler(this);
            }

        }

        public void OnTrackableStateChanged( TrackableBehaviour.Status previousStatus, TrackableBehaviour.Status newStatus){


        /*
        if(audio.isPlaying ){
            audio.Stop ();
        }*/ 

        if (newStatus == TrackableBehaviour.Status.DETECTED ||
                  newStatus == TrackableBehaviour.Status.TRACKED ||
                  newStatus == TrackableBehaviour.Status.EXTENDED_TRACKED) {

            allAudioSources = FindObjectsOfType (typeof(AudioSource)) as AudioSource[];
            foreach (AudioSource audioS in allAudioSources){
                audioS.Stop ();
            }
            textoLibro.text = "";

            if (!audio.isPlaying) {
                audio.Play ();
            } 

            //Colocamos el texto de la naración en pantalla.
            getOpenDb();

            string sqlQuery = "Select * From textoLibros WHERE nParrafo = "+ nParrafo +" AND idusuario = 0";
            dbcmd = dbconn.CreateCommand();
            dbcmd.CommandText = sqlQuery;
            reader = dbcmd.ExecuteReader ();
            while(reader.Read()){
                string names = reader.GetString (2);
                textoLibro.text = names;

                //Debug.Log (" Nombre"+ names);
            }

            imgEscena.sprite = Resources.Load<Sprite> ("escenas-RA/EscenaRa-01");

            getCloseDb ();

        } 
      }

    //
    //  Creamos la conexion con la bd SQlite
    //
    public void getOpenDb(){

        if (Application.platform != RuntimePlatform.Android) {

            conn = Application.dataPath + "/StreamingAssets/" + namedb;

            if(!File.Exists(conn)){
                File.Create (conn);
            }

        } else {

            conn = Application.persistentDataPath + "/" + namedb;

            if (!File.Exists(conn))
            {
                // if it doesn't ->
                // open StreamingAssets directory and load the db ->
                WWW loadDB = new WWW("jar:file://" + Application.dataPath + "!/assets/" + namedb);  // this is the path to your StreamingAssets in android
                while (!loadDB.isDone) { }  // CAREFUL here, for safety reasons you shouldn't let this while loop unattended, place a timer and error check
                // then save to Application.persistentDataPath
                File.WriteAllBytes(conn, loadDB.bytes);
            }
        }

        dbconn = new SqliteConnection ("URI=file:" + conn);
        dbconn.Open ();

    }

    //
    //Cerramos la conexión Sqlite
    //
    public void getCloseDb(){

        reader.Close ();
        reader = null;
        dbcmd.Dispose ();
        dbcmd = null;
        dbconn.Close ();
        dbconn = null;

    }

   }