What JPEG Stands For
JPEG is an acronym for Joint Photographic Experts Group, the ISO/IEC committee that standardised the format in 1992. The standard defines the compression algorithm; the file format itself is technically called JFIF (JPEG File Interchange Format), though colloquially everyone says JPEG or JPG.
Why Windows Used the Three-Letter Extension
Early versions of MS-DOS and Windows 3.x enforced the 8.3 filename convention- A maximum of eight characters for the name and three for the extension. Because .jpeg has four characters, software on those platforms shortened it to .jpg. Mac OS and Unix/Linux had no such restriction and historically used .jpeg.
When You Might Need the .jpeg Extension
Almost no modern software cares which spelling you use. Rare situations where .jpeg is specifically required include:
- Legacy web servers or CMS platforms whose MIME-type mapping only recognises
.jpeg - Certain older digital-asset-management (DAM) systems with hard-coded extension filters
- Some industrial or medical imaging devices with strict filename parsers
In practice, renaming photo.jpg to photo.jpeg is all that is needed.