JFIF to JPG

This is a naming problem masquerading as a format problem. JFIF stands for JPEG File Interchange Format, and it is the container that essentially every file you already call a JPG uses internally. The reason you suddenly have files ending in .jfif is a Windows registry quirk: certain combinations of Windows and Chrome register .jfif as the preferred extension for the image/jpeg MIME type, and from then on saved images get that extension instead of .jpg. The bytes are identical to what you would have got before. Unfortunately a lot of software checks the extension rather than the file contents — job application portals, older photo managers, e-commerce uploaders, school submission systems — and simply refuses. Renaming the file by hand often works, but it fails when the extension is hidden, when there are dozens of files, or when the receiving system also validates the contents.

You often can, and if you have one file and visible extensions it is the quickest fix. It breaks down at scale and in the cases where Windows hides extensions from you, so you end up with something called photo.jpg.jfif that is no better off. Converting also normalises the file: it is decoded and re-encoded as a standard baseline JPEG, which resolves the occasional case where the receiving software was objecting to something inside the file rather than to its name.

The underlying cause is a file-type association in the Windows registry, under the entry for the image/jpeg content type, where .jfif is listed as the default extension. Editing the registry fixes it permanently for future downloads but does nothing for the files you already have, and it is not something to attempt casually. Converting handles what is already on your disk, which is usually the immediate problem.

Because JFIF and JPG are the same underlying format, this conversion is close to a pass-through. The image is decoded and re-encoded once, so at a high quality setting the difference is imperceptible. Leave the quality slider high — there is no size problem to solve here, and this is not the moment to compress.

JFIF is not really a separate format — it stands for JPEG File Interchange Format, and it is the container that the overwhelming majority of files you already call JPGs are stored in. The confusion is purely about the file extension. Certain Windows and Chrome configurations save downloaded images as .jfif instead of .jpg, and although the bytes are a perfectly ordinary JPEG, a surprising amount of software refuses to open them purely because it does not recognise the extension.

JPG (also written JPEG) has been the default photograph format since 1992. It uses lossy compression tuned for the way human vision works — discarding fine colour detail the eye barely registers — which is why a photo saved as JPG can be a tenth the size of the same image as PNG. The trade-off is that it has no transparency channel and that every re-save degrades the image slightly, so it suits finished photographs rather than working files.