.JPG file signature
A JPEG image data file begins with the bytes FF D8 FF at the start of the file. The signature is the same whatever the file is named, which is why a renamed or extensionless JPEG file is still recognisable.
Signature
| Offset | Hex | ASCII |
|---|---|---|
| 0 | FF D8 FFThe fourth byte identifies the first marker: E0 (JFIF), E1 (Exif), DB, EE and others. |
MIME type: image/jpeg · usual extensions: .jpg, .jpeg
How to check a file's signature
Without installing anything: drop the file on our detector. It reads the bytes in your browser and shows the hex dump alongside the verdict; nothing is uploaded.
macOS and Linux (Terminal):
xxd -l 32 file.jpg
file file.jpgWindows (PowerShell):
Format-Hex -Path file.jpg -Count 32If the bytes do not match
A file named .jpg whose first bytes are something else is not a JPEG file. The common explanations are a wrong or deliberately misleading extension, a download that saved an HTML error page instead of the file, or a container such as ZIP wrapping the real content. The detector reports what the bytes say; the JPEG guide explains what a genuine file should contain.