apply soft edges to image using css

Given an image, is there a way to soften the edges using css? Or through some js library (although css would be preferred)? The idea is that the edges of the image should blur into transparency, so they fit in better with the background.

Example, original image:

Image with softened edges:

There are many similar questions asked on stackoverflow, however none (that I can find) offer an answer to do exactly this. Mostly they're concerned with blurring the whole image, or setting a semi-transparent border on the image, neither being what I'm looking for.