Know Your Library: How the libjpeg Version Influences Compression and Decompression Results

Introduced in 1991, libjpeg has become a well-established library for processing JPEG images. Many libraries in high-level languages use libjpeg under the hood. So far, little attention has been paid to the fact that different versions of the library produce different outputs for the same input. This may have implications on security-related applications, such as image forensics or steganalysis, where evidence is generated by tracking small, imperceptible changes in JPEG-compressed signals. This paper systematically analyses all libjpeg versions since 1998, including the forked libjpeg-turbo (in its latest version). It compares the outputs of compression and decompression operations for a range of parameter settings. We identify up to three distinct behaviors for compression and up to six for decompression.