session-android/res/layout/recipient_preference_photo_rail_item.xml

<?xml version="1.0" encoding="utf-8"?>
<org.thoughtcrime.securesms.components.SquareFrameLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginEnd="2dp"
        app:square_height="true">

    <org.thoughtcrime.securesms.components.ThumbnailView
            android:id="@+id/thumbnail"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:scaleType="centerCrop"/>

</org.thoughtcrime.securesms.components.SquareFrameLayout>