It might be very useful to b able to essentially "print" or "stamp" textual info onto an image, so that such things as date, or eve better, parts of a description, would appear in the lower left corner (for example), of an image. This would mean that the common viewer would instantly see the information, rather than having to bring up a metadata viewer.
This information would also be included in a hardcopy print.
Is anyone familiar with any techniques to do this programmatically, using exiftool?
It would be best if this could be a sort of toggle, where one could remove the information and still retain the unaltered original image.
Exiftool only edits metadata. It does not do any image editing.
You might want to look into ImageMagick (https://imagemagick.org/), which does edit image data and can read some metadata and place it on the image.
I use ImageMagick for my watermarks but I had a quick look around the internet for a simpler command.
I modified that to
convert leffe.jpg -gravity SouthEast -pointsize 50 -annotate +20+20 '%[EXIF:DateTime]' leffe2.jpg
See attached file for the result.
Terrific! Thanks!