I use exiftool from http://www.sno.phy.queensu.ca/~phil/exiftool/ Phil Harvey.
Download and install is easy and a description is on the site.
I wanted to remove the Image Description tag because Olympus does give this tag the value of OLYMPUS DIGITAL CAMERA. This Value is put into the caption if my wordpress blog images. And I did remove this caption by hand.
exiftool could do this in batch mode, but I am not sure it does. Still trying and testing
In Terminal: exiftool ~/Pictures/#name of directory#/ -EXIF:ImageDescription=Value
If you want to change a single file you can use #filename# in place of #name of directory#. Exiftool can help with a lot more exif and image related problems.
The classic WordPress dashboard does not make a caption when uploading an image, that is a very useful trick to avoid this Olympus tag in the caption.