Use android:scaleType="fitXY"
to keep the image fit the screen. change your ImageView to this.
<ImageView
android:id="@+id/ad_server_picture"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:scaleType="fitXY"
android:contentDescription="@string/ad_banner_image_description"
android:gravity="bottom|center_horizontal"
/>
HIH.