This software is a small patch to the Independent JPEG Group's JPEG software to enable lossless cropping of JPEG images.
Of course, cropping is never lossless as the region cropped is thrown away; however, jpegcrop ensures that the region of the image you keep is identical to that same region in the original.
The IJG's jpeglib includes a utility called jpegtran for doing lossless transformations on JPEG images.
It is this utility that is patched to include the cropping functionality.
The patch file modifies the files jpegtran.c,
transupp.h, and transupp.c. The output of
jpegtran -h is modifed to document the new behaviour. The
man page for jpegtran is not modified. Someone feel free to
update the man page.
Files available for download include: