Scaling animation for the Image looks strange

Rectangle {
    id: root
    color: "blue"
    width: 500
    height: 500
    Image {
        id: img
        source: "white_border.png"
        anchors.centerIn: parent

        NumberAnimation {
            id: anim
            running: true
            loops: Animation.Infinite
            to: 0.3
            property: "scale"
            target: img
            duration: 10000
        }
    }
}