<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" >
    <CheckBox
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:button="@drawable/check_selector"
        android:checked="true" />
</RelativeLayout>

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@drawable/checkok" android:state_checked="true"></item>
    <item android:drawable="@drawable/checkno" android:state_checked="false"></item>
</selector>