Basic CSS image swap on hover

HTML

<a id="MyImage" href="http://google.com">
        <img src="https://farm4.staticflickr.com/3041/2942361043_38a9b3d2ec.jpg" />
        <img src="https://lh3.googleusercontent.com/-mx9FmfkZ8AQ/AAAAAAAAAAI/AAAAAAAAABo/L-smk8cBu-g/s640/photo.jpg" />
    </a>

CSS

#MyImage img:last-child{display:none}
#MyImage:hover img:first-child{display:none}
#MyImage:hover img:last-child{display:inline-block}