ScrollView white space at bottom

Make your relative layout height match parent, also use android:fillViewPort = "true" in your scroll view

<RelativeLayout 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"
    tools:context=".showPictures">
    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:fillViewport="true">

//...

you can use this code to avoid extra padding on bottom of scroll view:

android:overScrollMode="never"