Example
<svg width="800px" height="600px">
<defs>
<filter id="focus-blur" >
<feDiffuseLighting result = "diffOut" diffuseConstant = "1" lighting-color="white">
<feSpotLight id="spotlight" x = "500" y = "100" z = "150" pointsAtX = "500" pointsAtY = "100" pointsAtZ = "0" specularExponent ="12" limitingConeAngle="70"/>
</feDiffuseLighting>
<feColorMatrix in="diffOut" result="alphaMap" type="luminanceToAlpha"/>
<feComponentTransfer in="alphaMap" result="invertlight">
<feFuncA type="table" tableValues="1 0 0"/>
</feComponentTransfer>
<feGaussianBlur in="invertlight" result="featherspot" stdDeviation="5"/>
<feComposite operator="xor" result="infocus" in2="SourceGraphic" in="featherspot"/>
<feGaussianBlur in="SourceGraphic" result="outfocus" stdDeviation="2"/>
<feComposite operator="over" in="infocus" in2="outfocus"/>
<feComposite operator="in" in2="SourceGraphic"/>
</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(#focus-blur)" 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)
