JPEG to JPG Without a Converter — Same Format, Just Rename (and Spot the .jpeg That's Really WebP)

JPEG and JPG are one format with two spellings

I copied a photo saved as photo.jpeg, renamed the copy to photo.jpg and compared them. Both were 36,816 bytes with the same SHA-256 hash (179cffca942d27d8…), and both start with FF D8 FF E0 00 10 4A 46 49 46 — the JPEG start-of-image marker followed by JFIF. A rename changes the name in the folder, not a single byte of the picture.

Outside Windows it's the same story. The Library of Congress format description for JFIF lists jpg, jpeg, jpe, jfif and others as extensions of one format with the MIME type image/jpeg, and Microsoft's list of common file name extensions describes jpg and jpeg with the same words: 'Joint Photographic Experts Group photo file'.

Microsoft's documentation on file names explains the three letters: the MS-DOS FAT file system allowed 8 characters for the name and 3 for the extension. Today's file systems keep long names but can still create an 8.3 alias. On this PC's drive C:, dir /x showed photo.jpeg as PHOTO~1.JPE and holiday photo.jpeg as HOLIDA~1.JPE; drive D: showed no short names at all — Microsoft notes the alias can be turned off per volume.

Rename one file in File Explorer

1. 1Make the extension visible: in File Explorer, select View > Show > File name extensions (Microsoft's own wording).
2. 2Select the file and press F2 (or right-click → Rename).
3. 3Change only .jpeg to .jpg and press Enter.
4. 4Windows warns that changing the extension might make the file unusable. For a real JPEG it doesn't — click Yes.

If a form rejects the renamed file, the extension wasn't the problem — the next section shows how to check what's inside.

When a rename isn't enough: a .jpeg that's really WebP or PNG

The extension is only a label. A file can end in .jpeg and hold WebP or PNG data — for example when someone renamed it by hand, or a tool kept the old name. To test this, I saved the same picture as WebP and as PNG, named both .jpeg, then renamed those to .jpg too. Explorer's Type column labeled every one of them a JPEG/JPG file by extension alone (here 'ALSee JPEG File', since ALSee is this PC's default viewer). The first bytes told the truth.

Open PowerShell in the folder (in Windows 11, right-click an empty area of the folder → Open in Terminal) and look at the first line of Format-Hex:

Format-Hex .\photo.jpeg | Select-Object -First 1

# 00000000   FF D8 FF E0 00 10 4A 46 49 46 00 01 01 00 00 01  .Ø.à..JFIF......

To check a whole folder, this reads only the first 4 bytes of each .jpg and .jpeg file and prints a True/False column:

Get-ChildItem -Filter *.jp*g | ForEach-Object {
  $fs = [IO.File]::OpenRead($_.FullName); $b = New-Object byte[] 4
  [void]$fs.Read($b, 0, 4); $fs.Close()
  $h = ($b | ForEach-Object { $_.ToString('X2') }) -join ' '
  [pscustomobject]@{ Name = $_.Name; First = $h; JPEG = $h.StartsWith('FF D8 FF') }
}

Name                  First        JPEG
----                  -----        ----
fake_png.jpeg         89 50 4E 47 False
fake_png_renamed.jpg  89 50 4E 47 False
fake_webp.jpeg        52 49 46 46 False
fake_webp_renamed.jpg 52 49 46 46 False
photo.jpeg            FF D8 FF E0  True
photo.jpg.jpeg        FF D8 FF E0  True
photo_renamed.jpg     FF D8 FF E0  True

For the False ones, convert instead of renaming. In Chromium 152 I gave a WebP and a PNG the type image/jpeg and the name disguised.jpeg; createImageBitmap — the call the Image Converter uses to read your file — decoded both by their contents. So the converter opens them despite the wrong name and saves a real JPG. For WebP files in general, see the WebP to JPG guide.

Rename a whole folder — and the file that gets skipped

In PowerShell, from inside the folder:

Get-ChildItem -Filter *.jpeg | Rename-Item -NewName { $_.BaseName + '.jpg' }

Or in Command Prompt: ren *.jpeg *.jpg. I ran both on copies of the same test folder: 20 files img01.jpeg–img20.jpeg, 3 in capitals CAM1.JPEG–CAM3.JPEG, and dup.jpeg sitting next to an existing dup.jpg. Each command renamed 23 of the 24 .jpeg files (PowerShell took 0.37 s), the capitals included — they became CAM1.jpg — because Windows matches names without regard to case.

dup.jpeg stayed behind. PowerShell printed Rename-Item : Cannot create a file when that file already exists. and Command Prompt A duplicate file name exists, or the file cannot be found. Neither overwrote dup.jpg, which is good — but in a big folder that one red line is easy to miss. This version picks the next free name instead:

Get-ChildItem -Filter *.jpeg | ForEach-Object {
  $new = $_.BaseName + '.jpg'; $i = 2
  while (Test-Path -LiteralPath (Join-Path $_.DirectoryName $new)) {
    $new = "$($_.BaseName) ($i).jpg"; $i++
  }
  Rename-Item -LiteralPath $_.FullName -NewName $new
}

In a folder with a.jpeg, b.jpeg, x.JPEG and dup.jpeg — where dup.jpg and dup (2).jpg already existed — it produced a.jpg, b.jpg, x.jpg and dup (3).jpg, and left both existing files untouched.

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