Move over, cruise ship photographers. A new type of enterprising shutterbug is on the tourist trail.

Vacation portrait photographers are independent entrepreneurs who approach tourists at public attractions and offer to snap group portraits. In a digital twist, tourists receive a card with a code number on it, and later, they can view the images online and decide if any of the prints are worth purchasing. The use of a code number to access the images protects a traveller's privacy, shielding the photos from the public eye.

The concept of vacation portraits has been floating around for a while, but it accelerated last September with the founding of the site Candidtag, the first major platform to promote the genre.

Since September, more than 100 photographers from 35 states have signed up with the site, covering many US-only cities, such as Austin, Boston, New York City, San Francisco, Minneapolis and Nashville. The site is run by Matt Wolin, a 28-year old Chicagoan, who is a software engineer by day and an aspiring professional photographer at night.

Jimmy and Jackie Dietzen encountered the service last September, when they were visiting Chicago's Grant Park with their two young children. The Denziens later purchased an image from Wolin’s site.

“Sure, I have a camera on my phone,” Jimmy said. “But this was a professionally-shot image, which looks a hundred times better than if we handed our cell phone to someone.”

Candidtag doesn't vet the portfolios of its photographers -- essentially, anyone with a camera can sign up – so photo quality can vary. There is always the chance that when travellers have their photos taken, the images they see online might not be good enough to order. The printing and shipping, however, is fulfilled by Adorama, a New York City lab that has gotten high ratings from consumers.

For tourists, common sense precautions apply in dealing with a solicitation from a stranger, regardless of whether he or she is holding a fancy camera. Travellers should never hand over money or contact information in person, and they should also watch out for photography being a ruse to distract them while being pick-pocketed.

Presently there is no way for a traveller to hire someone’s services through the site. Photographers and travellers have to stumble upon each other in a bit of serendipity.

Sean O'Neill is the tech travel columnist for BBC Travel