Images saved with JPG extensions that aren’t

More images I save from sites thesedays don’t end up showing thumbnails in file browsers. For example, Dolphin on KDE: And the Finder on macOS: Why is that? I assumed maybe the embedded thumbnails were getting corrupted somehow, or there was a resource fork issue saving images on my OpenZFS volumes over Samba. No, turns out it’s much simpler than that. Browsers are getting the file extension wrong, as is the case with this tea photo: $ file floejt-black-tea.jpg ==> floejt-black-tea.jpg: ISO Media, AVIF Image Another common one is webp: $ file ipmi.jpg ==> ipmi.jpg: RIFF (little-endian) data, Web/P image, VP8 encoding What I suspect is happening is web servers and browsers are negotiating supported file formats, and the server is delivering an alternative format to save bandwidth, but the browser is still saving the file with the original JPEG extension. Hence the mismatch. Interestingly, it doesn’t happen all the time. Some images I download are saved with the correct extension, even…