Version: 1.2.0 (using KDE KDE 3.4.0) Installed from: Unspecified Linux0 IPTC metadata could be better place for comment data than JPEG comment field or EXIF headers because growing number of software is adopting the standard and because IPTC provides other useful fields like copyright, keywords, location, contact etc. information. For more information, see: http://libiptcdata.sourceforge.net/
Taking this issue, I want to get back an old thread of 2009: http://thread.gmane.org/gmane.comp.kde.gwenview/2271/ There we talked about saving comments directly into JPG image file, besides doing it into Nepomuk also. May be an option to choose the JPG header where to save the comment (JPEG, EXIF or IPTC) would be great. This bug could be related with the more recent one: Bug 330495, which adds the [may be better or more appropriate] field UserComment, that supports utf-8 encoding.
I vote for letting the user choose where to meta information should be stored and edited. Also have a look at: Bug 426307 - quick edit Exif/IPTC/XMP tags tags https://bugs.kde.org/show_bug.cgi?id=426307