image-dired-cmd-write-exif-data-options

image-dired-cmd-write-exif-data-options is a variable defined in `image-dired.el'.
Its value is

"%p -%t=\"%v\" \"%f\""

Documentation:
Format of command used to write EXIF data.
Available options are %p which is replaced by
`image-dired-cmd-write-exif-data-program', %f which is replaced by
the image file name, %t which is replaced by the tag name and %v
which is replaced by the tag value.

You can customize this variable.