This should give you the required layout:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
<ImageView
android:id="@+id/flag"
android:layout_width="fill_parent"
android:layout_height="250dp"
android:layout_alignParentLeft="true"
android:layout_alignParentRight="true"
android:scaleType="fitXY"
android:src="https://stackoverflow.com/questions/19065232/@drawable/ic_launcher" />
<TextView
android:id="@+id/textview"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_marginTop="20dp"
android:layout_centerHorizontal="true" />
</RelativeLayout>
Play with the android:layout_marginTop="20dp" to see which one suits you better. Use the id textview to dynamically set the android:text value.
Since a RelativeLayout stacks its children, defining the TextView after ImageView puts it ‘over’ the ImageView.
NOTE: Similar results can be obtained using a FrameLayout as the parent, along with the efficiency gain over using any other android container. Thanks to Igor Ganapolsky(see comment below) for pointing out that this answer needs an update.