Wikivoyage:Comments in image files

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

On Linux

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

On Windows

for testing only

On Linux

PPM file to JPEG file

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

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

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.