Uniform collar image.
Tom Schmidt was a 24th century Human, a Starfleet commander and xenobiologist, considered an expert on the Borg.
Biography
He traveled with Admiral Kathryn Janeway on the Einstein to the Borg cube discovered in the Alpha Quadrant. (TNG novel: Before Dishonor)
Appendices
Background
For the purposes of this wiki, a full commander's rank insignia is shown, but it is just as likely Schmidt was a lieutenant commander addressed as "commander". No insignia was described in the novel.