wrjpgcom

wrjpgcom [options] filename.jpg

-comment "text"
    Specifies the comment string to be written into the JPEG file. Enclose the text in quotes, especially if it contains spaces or special characters.

-c "text"
    A shorthand alternative for -comment, specifying the comment string to be written.

-replace
    Replaces all existing comment markers in the file with the new comment provided by -comment or -c. If no new comment is specified, this option has no effect.

-insert
    Inserts the new comment before any existing comment markers in the file. If no new comment is specified, this option has no effect.

-append
    Appends the new comment after any existing comment markers in the file. If no new comment is specified, this option has no effect.

-dump
    Prints all existing comment markers from the specified JPEG file to standard output. No new comment is written when this option is used. This is useful for inspecting current comments.

-q
    Operates in quiet mode, suppressing non-critical messages and warnings during execution.

-?
    Displays a help message with usage instructions and available options, then exits.

--help
    Displays a comprehensive help message with usage instructions and available options, then exits.

--version
    Shows the version information for the wrjpgcom utility, then exits.

filename.jpg
    The path to the JPEG image file to be processed. This argument is mandatory.

wrjpgcom is a command-line utility designed to manage textual comments embedded within JPEG image files. JPEG files can contain special markers, known as Comment (COM) markers, which allow arbitrary textual information to be stored alongside image data without affecting the image display. This utility enables users to add new comments, replace existing ones, or append comments to a JPEG file. It can also be used to simply dump all existing comments from a specified JPEG file to standard output, making it useful for inspecting metadata. wrjpgcom is a handy tool for adding copyright notices, descriptions, or any other relevant text directly into the image file itself, which can be useful for organization or preserving metadata across various systems.

The command directly modifies the JPEG file, inserting or updating the comment markers according to the specified options.

The maximum length of a single comment marker can be limited by the JPEG standard, typically around 64KB, though most practical uses won't exceed this. wrjpgcom specifically handles JPEG Comment (COM) markers; it does not manage other forms of metadata like EXIF, IPTC, or XMP. For comprehensive metadata management, dedicated tools like exiftool should be used. Always back up critical images before modifying them with any command-line tool, as direct file manipulation carries inherent risks.

JPEG files allow for 'Comment' (COM) markers, which can store arbitrary text. These comments are typically ignored by standard image viewers and processing software, making them a discreet way to embed metadata, copyright notices, or internal notes directly into the image file without altering its visual representation or critical EXIF data.

When using -insert or -append, wrjpgcom adds the new comment without removing existing ones, preserving all previous comments. The -replace option is the only one that will remove all prior comments before writing the new one, making it a destructive operation for existing comment metadata. If no option for placement (-replace, -insert, -append) is specified, the default behavior often varies between versions or implicitly appends the comment.

The wrjpgcom utility is typically part of the jpeginfo package or similar collections of tools that interact with the libjpeg library, a foundational component for JPEG processing on Unix-like systems. Its development has closely paralleled the evolution of the libjpeg library itself, which provides the underlying JPEG compression and decompression functionalities. While not as widely used for general image manipulation as tools like jpegtran, wrjpgcom fills a specific niche for managing the lesser-known, but often useful, comment markers within the JPEG standard. It has been a stable and long-standing utility in the ecosystem of JPEG processing tools, offering a straightforward way to embed textual metadata directly into image files.

rdjpgcom(1), jpegtran(1), cjpeg(1), djpeg(1), exiftool(1)