Business headshot photography sounds like something that would not be very profitable. However, this type of photography has dozens of applications, more than you probably realized. In fact, you may engage the services of a business photographer in all of the following categories.
At the DMV/DOT
They cannot put a headshot on your ID or license without a photographer. The person taking the headshots is usually the same two or three people all the time; you will never see any of the other employees at the DMV/DOT taking the headshots. Could these people be professional photographers? Maybe they are, or maybe they are professionals trained to take business-related headshots. Either way, everyone's picture ends up on their IDs/licenses.
At a Passport Location
From drug stores to post offices, passport photos are taken. These headshots are required for every passport everyone ever applies for and will need. The photos have to be retaken every ten years because of how rapidly people's appearances change. Regardless of the location where the passport photos are taken, these people are required to know something about photography and something about professional efforts to take a good picture.
For Business ID Badges
People use ID badges to swipe in and out of work now. Actual punch clocks with faceless names attached to paper cards are gone. You have to have your headshot taken, applied to an ID badge, and logged into a computer just to get through the front entrance. A business photographer is hired to come in on certain days after mass hiring events and take several headshots. On occasion or as the need arises, the photographer may need to take one or two headshots of a couple of people that are hired outside of mass hiring events.
For Criminal Mugshots
Sometimes police officers take these photos, but the rest of the time a business photographer takes all of the mugshots of the possible criminals charged with crimes during a "booking." This is an ongoing gig for a business photographer, and he/she may be required to take badge and/or employee headshots for employee work files too. The work is rather steady, so many police stations tend to hire a professional photographer to remain on city payroll for this position.
For School Photos
Thousands of kids get their picture taken on "picture day" every year. In some school districts, the pictures may be taken twice a year; once in the fall and once in spring. In middle schools and high schools, headshot photographers also make student and staff IDs.