Possibly the easiest way to achieve such an effect is to overlay a rounded rectangle with a transparent black outline over the image. However, you will also need to wrap the element in another container with overflow set to hidden to limit the backdrop to the image.
Here is a quick demo:
.wrapper {
position: relative;
overflow: hidden;
width: 500px;
height: 300px;
}
.circle {
position: absolute;
border-radius: 100%;
outline: rgba(0, 0, 0, 0.5) 100vmax solid;
height: 200px;
width: 200px;
top: 50px;
left: 150px;
}
<div class="wrapper">
<div class="circle"></div>
<img class="image" src="https://picsum.photos/500/300">
</div>