<div id="container">
  <div class="blurme"></div>
</div>

div#container{
  width:300px;
  height:200px;
  overflow:hidden;
  position:relative;
}
div#container .blurme{
  width:100%;
  height:100%;
  background: url('https://placeimg.com/640/480/any') no-repeat;
  background-size:cover;
  transition:filter .3s ease;
}
div#container:hover .blurme{
  filter:blur(5px);
  transition:filter .3s ease;
}  

External CSS

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External JavaScript

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