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Wikivoyage:Comments in image files Voyage Tips and guide

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    The two image file formats most important for us, JPEG and PNG, both can contain comments. If you are trying to find the copyright holder of some image you may be lucky enough to find some hint in the image file's comment. Many image processing programs are able to show them.

    Reading the Comment

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    On Windows

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    On Mac

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    On Linux

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    Open a shell and type

    jpegtopnm -comments image1.jpeg > /dev/null
    

    The comment of the image file image1.jpeg is written to standard error. In order to find the comment of a PNG file, type

    pngtopnm -text commentfile image1.png > /dev/null
    

    The comment is written into the file commentfile.

    To read comments added in a jpeg file, use the command line tool rdjpgcom.

    rdjpgcom -verbose image_with_comment.jpeg
    

    Writing a Comment

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    On Windows

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    for testing only

    On Mac

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    On Linux

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    PPM file to JPEG file

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    Open a shell and type

    pnmtojpeg -comment "Author: Emma Peel; Licence: Attribution-ShareAlike 1.0" image1.ppm > image1.jpeg
    

    Thus, the new JPEG file image1.jpeg with the above comment is created from the PPM file image1.ppm.

    PPM file to PNG file

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    In order to create a PNG file with comment you first need to create a comment file in the format

    Key1       Value1
    Key2       Value2
    Key3       Value3
     .
     .
    

    Assumed we had a file called comment-file with the following contece:

    #>cat comment-file
    Author:   Emma Peel
    Licence:  Attribution-ShareAlike 1.0
    #>
    

    we create the new PNG file by typing

    pnmtopng -text comment-file image1.ppm > image1.png
    

    Add comment to existing JPEG files

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    The command line tool 'wrjpgcom' can be used to add comments to existing JPEG files.

    Open a shell and type

    wrjpgcom -comment "Author: Emma Peel; Licence: Attribution-ShareAlike 1.0" image1.jpeg > image_with_comment.jpeg
    

    If there is an existing comment block (even an empty one) in the JPEG file, you must add the option '-replace' for this to work:

    wrjpgcom -replace -comment "Author: Emma Peel; Licence: Attribution-ShareAlike 1.0" image1.jpeg > image_with_comment.jpeg
    

    Please refer to the man page for more details.


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