Should you rename that image BWC09881.jpg to blue-widget-internal-view.jpg to add an additional flag as to what it’s about? Google has said the equivalent of “you may as well” recently, but it’s probably not worth going back to change existing image files. The more important thing is to ensure the alt text is complete and descriptive, and that the page text surrounding the image also describes it. However, for new images you’re uploading to the site, it’s a good idea to change the file name to something comprehensible. As with everything else in SEO nowadays, if it’s helpful for humans, it’ll be approved of by Google.