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.

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

On Windows
for testing only

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:

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

we create the new PNG file by typing

pnmtopng -text comment-file image1.ppm > image1.png de:Project:Kommentare in Bildern

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.