Use the new CSS filter property.

Supported by webkit browsers, Firefox 34+ and Edge.

You can use this polyfill that will support FF < 34, IE6+.

You would use it like so:

/* Use -webkit- only if supporting: Chrome < 54, iOS < 9.3, Android < 4.4.4 */

.shadow {
  -webkit-filter: drop-shadow( 3px 3px 2px rgba(0, 0, 0, .7));
  filter: drop-shadow( 3px 3px 2px rgba(0, 0, 0, .7));
  /* Similar syntax to box-shadow */
}
<img src="https://upload.wikimedia.org/wikipedia/commons/c/ce/Star_wars2.svg" alt="" class="shadow" width="200">

<!-- Or -->

<svg class="shadow" ...>
    <rect x="10" y="10" width="200" height="100" fill="#bada55" />
</svg>

This approach differs from the css box-shadow effect in that it accounts for opacity and does not apply the drop shadow effect to the box but rather to the outline of the svg element itself.

Please Note: This approach only works when the class is placed on the <svg> element alone. You can NOT use this on an inline svg element such as <rect>.

<!-- This will NOT work! -->
<svg><rect class="shadow" ... /></svg>

Read more about css filters on html5rocks.