Lepton

File Format
Name	Lepton
Ontology	Electronic File Formats Compression Lepton ; ; ;
Extension(s)	.lep, .ujg
Released	2016

Lepton is a special-purpose compression algorithm and file format, developed by Dropbox. It only compresses JPEG files.

Identification

Files begin with 0xcf 0x84 (lepton), or 0xce 0xb6 (zlib compressed lepton).

The lepton software appears to also support a format it calls "UJG", which starts with ASCII "UJ".