That format is actually properly called JPEG (Joint Photographic Experts Group), and the extension '.jpeg' is commonly used on *nix OSes. Using '.jpg' only became the standard on DOS/Windows in conformance with the old 8.3 filename constraint -- the same reason HTML files are often '.htm' rather than '.html' on Windows.
It’s like .JPG files: sure, you can call them ‘Jay Pee Gee’ files, but it’s easier to call them ‘Jay-Pegs’.