JPEG images provide the option of adding metadata to the image file.  This option is frequently used to add EXIF data covering a range of information on such details as the camera settings and location.  However, not all the data added has to be in the EXIF format and there are some applications that require the provision of other metadata from the  JPEG  file.  This includes the possibility of adding comments to the file.   The command line application exiv2 is a useful tool for reading and editing EXIF and other metadata held within JPEG files.

I have had a recent need to add non EXIF comments to JPEG files and have used exiv2 for that purpose.  However, to streamline the process I have developed a short GUI application written in Python application using Illumination Creator from RadicalBreeze.  The application is called JpegComment.  It is freely  downloadable from the link on this page and can be used without any warranty at your own discretion under the GPL2 licence.  Please also feel free to download the icon (right click and Save Image). To  run this application ensure that it is placed in a location that can be found in the PATH variable and ensure that it has executable permissions (right click in Nautilus and go to the Permissions tab).  The application also requires exiv2, Imagemagick and xwininfo to have been downloaded and installed on your computer....this can be done through your package manager.  (The application is currently at alpha version 0.4.2)