However, you can do more than that just a simple image, Android allow you to change the button’s image depends on different states like button is focused or button is pressed.
res/drawable/new_button.xml
<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
<item android:drawable="@drawable/button_pressed_yellow"
android:state_pressed="true" />
<item android:drawable="@drawable/button_focused_orange"
android:state_focused="true" />
<item android:drawable="@drawable/button_normal_green" />
</selector>
For example in usage of your button:
<Button
android:id="@ id/imageButtonSelector"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="@drawable/new_button" />