Edit in JSFiddle

<h1>Original</h1>
<img width="200" height="200" src="https://avatars3.githubusercontent.com/u/5305599">

<h1>Blur boundaries</h1>
<figure class="container">
  <img class="image" src="https://avatars3.githubusercontent.com/u/5305599">
</figure>

body {
  color: white;
  background-color: gray;
}

.container {
  position: relative;
  width: 200px;
  height: 200px;
}
.container::after {
  position: absolute;
  content: '';
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
  box-shadow: inset 0 0 15px 15px gray;
}
.image {
  width: 100%;
  height: 100%;
}