Delete all meta information
exiftool -all= dst.jpg
Delete all meta information from an image and add a comment back in
exiftool -all= -comment='lonely' dst.jpg
Delete Photoshop meta information from an image
exiftool -Photoshop:All= dst.jpg
Extract information from an embedded thumbnail image
exiftool image.jpg -thumbnailimage -b | exiftool -
Add an IPTC keyword in a pipeline, saving output to a new file
cat a.jpg | exiftool -iptc:keywords+=fantastic - > b.jpg