Example
<svg width="800px" height="600px">
<defs>
<filter id="greyscale">
<feColorMatrix type="matrix"
values="0 1 0 0 0
0 1 0 0 0
0 1 0 0 0
0 0 0 1 0"/>
</filter>
</defs>
<image xlink:href="https://upload.wikimedia.org/wikipedia/commons/a/af/Fruit_Stall_in_Barcelona_Market.jpg" x="20px" y="20px" width="300px" height="200px" preserveAspectRatio="xMinYMin meet" />
<image filter="url(#greyscale)" xlink:href="https://upload.wikimedia.org/wikipedia/commons/a/af/Fruit_Stall_in_Barcelona_Market.jpg" x="340px" y="20px" width="300px" height="200px" preserveAspectRatio="xMinYMin meet"/>
</svg>
(Source image by Daderot at Wikimedia Commons)
