This is a cool way to add captions to your scanned photos without having to rely on embedded metadata. In other words, this way would allow you to have the written caption as a part of the JPEG or TIFF file itself. The main advantage to this idea is not losing your captions over the years (possibly even centuries) should an application “accidentally” delete or write over the metadata contents.
Programs change, data conversion can get lost — this way your caption is part of the photo itself and thus your written information for your photos shouldn’t be lost (the only way this could happen would be to crop it off from the photo). So years from now, people will know who or what is in your photo, and/or any other tidbit you might want to include.