<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <!-- we are using ImageView for displaying image-->
    <ImageView
        android:id="@+id/rImage"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="20dp" />

</LinearLayout>

import android.os.Bundle;
import android.widget.ImageView;
import android.widget.Toast;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;
import com.squareup.picasso.Picasso;

public class MainActivity extends AppCompatActivity {

    // Initializing the ImageView
    ImageView rImage;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // getting ImageView by its id
        rImage = findViewById(R.id.rImage);

        // we will get the default FirebaseDatabase instance
        FirebaseDatabase firebaseDatabase = FirebaseDatabase.getInstance();

        // we will get a DatabaseReference for the database root node
        DatabaseReference databaseReference = firebaseDatabase.getReference();

        // Here "image" is the child node value we are getting 
        // child node data in the getImage variable
        DatabaseReference getImage = databaseReference.child("image");

        // Adding listener for a single change 
        // in the data at this location.
        // this listener will triggered once 
        // with the value of the data at the location 
        getImage.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                // getting a DataSnapshot for the location at the specified
                // relative path and getting in the link variable
                String link = dataSnapshot.getValue(String.class);

                // loading that data into rImage 
                // variable which is ImageView
                Picasso.get().load(link).into(rImage);
            }

            // this will called when any problem
            // occurs in getting data
            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
                // we are showing that error message in toast
                Toast.makeText(MainActivity.this, "Error Loading Image", Toast.LENGTH_SHORT).show();
            }
        });
    }
}