From The Verge:
If you’ve ever needed to quickly remove the background of an image you know it can be tedious, even with access to software like Photoshop. Well, Remove.bg is a single-purpose website that uses AI to do the hard work for you. Just upload any image and the site will automatically identify any people in it, cut around the foreground, and let you download a PNG of your subject with a transparent background.
As the article notes, Remove.bg is often useful but is far from perfect.