Free, portable C code for JPEG compression is available from the Independent
JPEG Group.  Source code, documentation, and test files are included.
Version 6b is available from ftp.uu.net:/graphics/jpeg/jpegsrc.v6b.tar.gz.
If you are on a PC you may prefer ZIP archive format, which you can find at
ftp.simtel.net:/pub/simtelnet/msdos/graphics/jpegsr6b.zip (or at any
Simtel mirror site).  On CompuServe, see the Graphics Learning forum
(GO CIS:LEARN), library 12 "JPEG Tools", file jpegsr6b.zip.

The IJG code includes a reusable JPEG compression/decompression library,
plus sample applications "cjpeg" and "djpeg", which perform conversion
between JPEG JFIF format and image files in PPM/PGM (PBMPLUS), BMP,
Utah RLE, and Targa formats.  A third application "jpegtran" provides
lossless transcoding between different JPEG formats --- for example, it can
convert a baseline JPEG file to an equivalent progressive JPEG file.
jpegtran can also do lossless rotation and flipping of JPEG files.  Two
small applications "wrjpgcom" and "rdjpgcom" insert and extract textual
comments in JFIF files.  The package is highly portable; it has been used
successfully on many machines ranging from Apple IIs to Crays.

The IJG code is free for both noncommercial and commercial use; only an
acknowledgement in your documentation is required to use it in a product.
(See the README file in the distribution for details.)

The IJG code has recently been translated into Pascal --- see
ftp.simtel.net:/pub/simtelnet/msdos/turbopas/pasjpg10.zip.  This version
has been tested under Turbo Pascal and Delphi, and it should be portable
to compatible Pascal compilers.


A different free JPEG implementation, written by the PVRG group at Stanford,
is available from havefun.stanford.edu:/pub/jpeg/JPEGv1.2.1.tar.Z.  The PVRG
code is designed for research and experimentation rather than production
use; it is slower, harder to use, and less portable than the IJG code, but
the PVRG code is easier to understand.  Also, the PVRG code supports (the
original form of) lossless JPEG, while the IJG code does not.  But PVRG does
not support progressive JPEG.

There's also a lossless-JPEG-only implementation available from Cornell,
ftp.cs.cornell.edu:/pub/multimed/ljpg.tar.Z.  Caution: the Cornell coder
is known to have bugs for 16-bit data.

Neither the PVRG nor Cornell codecs are being actively maintained, but the
IJG code is.