public class MySOEditor : Editor
{
    SerializedProperty mySprite;

    void OnEnable()
    {
        mySprite = serializedObject.FindProperty("mySprite");
    }

    public override void OnInspectorGUI()
    {
        serializedObject.Update();

        EditorGUILayout.PropertyField(mySprite, GUIContent.none, GUILayout.Width(128), GUILayout.Height(128));

        serializedObject.ApplyModifiedProperties();
    }
}