OmniImageFilter is a filter package that converts NeXTStep TIFF to and from
about 30 image formats.  It reads JPEG but does not write it.  It works with
most NeXTStep programs that handle drag-and-drop.  OmniImage is a simple
image viewer that uses the filter package.  Both are free.  Available from
ftp://ftp.omnigroup.com/pub/software/ and
ftp://ftp.omnigroup.com/pub/software/.

ImageViewer is a PD utility that displays images and can do some format
conversions.  The current version reads JPEG but does not write it.
ImageViewer is available from the NeXT archives at sonata.cc.purdue.edu and
ftp://cs.orst.edu/pub/next/3.0/bin/.  Note that there
is an older version floating around that does not support JPEG.

The "imagetools" archive at ftp://ftp.thoughtport.com/pub/next/graphics/ includes
NeXTStep compiled binaries for a wide array of free image manipulation tools
including the IJG JPEG tools.

NeXTStep includes built-in support for TIFF/JPEG, but not for the
Usenet-standard JFIF format.  Be warned that the TIFF/JPEG standard is
about to change away from the flavor currently produced by NeXTStep,
so compatibility with other platforms is doubtful.