What is a .jpg file?

You have a JPG. You definitely have a JPG. Every photo on every social media feed, every product image on every shopping site, every picture your phone has ever texted — odds are, it was a JPG. The format has been the default for photographs since 1992, and nothing has come close to dethroning it.

JPG works by throwing away visual information the human eye is unlikely to notice — that's lossy compression. The file gets dramatically smaller and you almost never see the difference. The catch is that every time you re-save a JPG, it loses a little more. Save it ten times and you'll start to see fuzzy edges and colour banding, like a photocopy of a photocopy. This is why photographers shoot in RAW and only export to JPG at the very end.

Every device on earth opens JPG. Every app, every browser, every printer. If you need transparency, use PNG. If you need smaller files for the web, consider WebP. But for photographs where compatibility matters more than anything else, JPG is still the answer it was thirty years ago.