jpegtran

Mirror an image horizontally or vertically

$ jpegtran -flip [horizontal|vertical] [path/to/image.jpg] > [path/to/output.jpg]

$ jpegtran -rotate [90|180|270] [path/to/image.jpg] > [path/to/output.jpg]

$ jpegtran -transpose [path/to/image.jpg] > [path/to/output.jpg]

$ jpegtran -grayscale [path/to/image.jpg] > [path/to/output.jpg]

$ jpegtran -crop [W]x[H]+[X]+[Y] [path/to/image.jpg] > [path/to/output.jpg]

$ jpegtran -crop [W]x[H] -outfile [path/to/output.jpg] [path/to/image.jpg]

jpegtran [options] [file]

jpegtran performs lossless transformations on JPEG images. Unlike re-encoding, these operations work directly on the DCT coefficients, preserving image quality completely.
Supported lossless operations include rotation (in 90-degree increments), flipping, transposition, grayscale conversion, and cropping (on MCU boundaries). The tool can also optimize or convert between baseline and progressive formats.

-flip horizontal|vertical

Mirror the image

Rotate clockwise by specified degrees

Transpose across main diagonal

Transpose across anti-diagonal

Convert to grayscale

Crop to width W, height H, at offset X,Y

Write output to specified file

Optimize Huffman tables

Create progressive JPEG

Crop dimensions may be adjusted to MCU (Minimum Coded Unit) boundaries. Some transformations may require -trim to discard partial edge blocks. Output goes to stdout by default; redirect or use -outfile.

jpegtran is part of libjpeg/libjpeg-turbo, the reference JPEG library. The original libjpeg was developed by the Independent JPEG Group starting in 1991.

cjpeg(1), djpeg(1), convert(1)