JPG, JPEG, JFIF and JPE Explained

The short history

The Joint Photographic Experts Group published the JPEG compression standard in 1992. It described how to compress an image but not how to store one in a file, so a companion specification called the JPEG File Interchange Format — JFIF — defined the actual container. Essentially every JPEG you have ever seen is a JFIF file.

The extension varies for a much duller reason. MS-DOS and early Windows allowed only three characters after the dot, so .jpeg became .jpg. Unix systems had no such limit and kept .jpeg. Both stuck, and .jfif and .jpe turn up as well.

They are the same file

Rename a .jfif to .jpg and it still opens, because the bytes inside were always a JPEG. This is the one case where renaming an extension genuinely works — and it is the exception that proves the rule, since renaming a .heic or a .webp to .jpg achieves nothing at all.

Why you suddenly have .jfif files

This catches people out because it appears without warning. Saving an image from Chrome or Edge on Windows sometimes produces a .jfif rather than a .jpg, depending on how the server described the file and what the Windows registry has associated with the JPEG media type. It is a Windows registry quirk rather than a browser bug, and it can start happening after an update with no other change.

Everything about the file is normal. It opens in every image viewer. It just carries an extension that some upload validators have never heard of.

Fixing a rejected .jfif

• Rename it. Change .jfif to .jpg in File Explorer. You may need to turn on file extensions under the View menu first. This works because the contents really are a JPEG.
• Or re-save it. Opening the file and exporting as JPG rewrites it cleanly and removes any doubt. This is the safer option if the file is going somewhere fussy.
• Or stop it happening: in Windows, editing the registry entry that associates image/jpeg with the .jfif extension changes the default back to .jpg. Worth doing if it is constant.

What actually differs between JPEG files

Since the extensions are interchangeable, the real differences between two JPEG files are inside them, and these are the ones that affect quality and compatibility.

• Quality setting — how aggressively the encoder discarded detail. This is the big one.
• Chroma subsampling — usually 4:2:0, which halves colour resolution. Fine for photographs, visibly bad on red text.
• Progressive versus baseline — progressive files load in increasing detail and are often slightly smaller. Universally supported.
• Colour profile — an embedded profile such as sRGB or Adobe RGB. Files saved in Adobe RGB look flat in software that ignores profiles.
• EXIF metadata — camera, date, settings and often GPS coordinates.

Which extension should you use?

Use .jpg. It is the most widely recognised, it is what every upload form expects, and no system in use today rejects it. There is no technical advantage to .jpeg and a real practical disadvantage to .jfif, however standards-correct the name is.