More than 41 million people in the United States have posted their profile on dating websites - and yet only a small percentage seem to know how to snap a good picture of themselves.

Selfie in the mirror? Bad idea. Jumping a mogul from far, far away? Uh-uh. Artsy picture with moody shadows? Nope.

And so another industry has been born: professional profile-picture photography. Not to be confused with Glamour Shots, these photos fall somewhere between an actor head shot and an exterior portrait, said Gordon Gooch, founder of DatingHeadshots.com.

"It's nothing that could ever be confused with your yearbook photo or your last trip to the DMV - what everyone wishes that they could shoot if they understood the 'rule of thirds,' angle of light, and body positioning," he said.

Steven Goldblatt started doing work in 2009 for lookbetteronline.com, which contracts photographers in the U.S. and Canada to take dating website shots for clients.

"You want impact - good color, good composition, and a good-quality image," said Goldblatt, a professional photographer for 35 years in Blue Bell. "If you want to make an impression on someone, it makes sense to have a good photograph."

Carol Turner, "a young 66" from Teaneck, N.J., discovered the power of first impressions when she sought help from a professional photographer in October 2013 for online profile pics.

She hadn't gotten any responses the year previous, but the very first day her new pictures went up, she got well over 100 hits - 96 on blackpeoplemeet.com alone.

"If you want to meet someone that is presentable and professional, then your pictures should be likewise," she said. "Most of my 'flirts' were about my photos - many men said I had a million-dollar smile. And I never smiled in a photo before."

After e-mails, phone calls, and dates with several suitors, Turner is now in a relationship. "The photo was the driving factor," she said.

Jason Lucas, 42, an online-dating-site user for two years, recently traveled from his Harrisburg home to Philadelphia to see a professional photographer who specifically advertised online dating shots. About 80 pictures later, the 10 best went up online, and the response rate to his profile doubled, from about five a week to 10.

"Most people aren't a very good judge of what makes them attractive," said Grant Langston, eharmony.com vice president of brand marketing. "An objective person can say, 'Don't wear that, it's not flattering,' or 'Move your head in this direction.' That objective perception of what makes you attractive is really the magic of the process."

When eharmony.com launched in 2000, virtually no one used professional pictures, Langston said. But now about 20 percent do, a number that started growing in earnest three or four years ago. Langston attributes the growth to a decreased stigma regarding online dating in general.

In the company's spin-off, eh+, a matchmaking service, consultants help clients find their perfect dates for a $5,000 fee.

"We push for professional photos because it makes such a difference in how people react to the client," Langston said. "Using professional photos increases their success rate every single time."

Match.com, too, has seen an increase in the use of professional photos over the last five years, according to Bela Gandhi, spokeswoman for match.com and founder of smartdatingacademy.com, the Chicago-based matchmaking site she launched in 2009.

"Our Smart Dating Academy business has doubled year over year, and every one of those clients is going with professional photos," she said. "Good photography is part art and part science. People don't usually sit on a vessel of great photos of just themselves. Men and women are both visual so it's imperative that they have professional photos."

Online daters are catching on. DatingHeadshots.com has grown between 25 and 33 percent year-over-year since its launch in 2007, after Gooch had a match.com event in his New York gallery.

"Some of the match.com clients said they wished they could get great pictures for their dating profiles," he recalled. "Ding! The lightbulb went off."

Gooch struck a deal with match.com to offer their clients profile photos, and now the website serves the top 50 online dating cities throughout the U.S. and Canada - Philadelphia routinely ranks in the top 10 - with several thousand photographers on call.

Gooch's clientele is generally older than 30 and as old as their late 70s, with disposable income to afford in-studio shots (starting at $159, offering 50 photos and two wardrobe changes) and on-location shots ($159 to $1,000). If that's too pricey, the site will give you advice about your own photos for just $5.

Of course, once you're on that first date, the picture no longer matters, "but it gets you that date," Gooch insisted.

In June, Max Schwartz, a Brooklyn-based photographer, launched tinderheadshots.com (not associated with the Tinder app that lets users evaluate other people through swipes to their photos - right means you "like" someone, left means you don't).

Initially it was a joke.

"I randomly took a picture of one of my coworkers and he put it on his Tinder, and he started getting a lot more swipe rights," he recalled. Schwartz created humorous Craigslist ads promoting his online dating photo service and attracted attention, both positive and negative. "There are a lot of websites making fun of it," he admitted. But as they say, no press is bad press, and Schwartz's site is now growing. When a YouTube video interviewing him drew 80,000 views in a month, he realized that it was no longer a joke.

Without giving up his day job, Schwartz is now shooting about 10 clients each weekend for online dating photos: one photo for $75, or a package of three for $150.

Lookbetteronline.com, cofounded by David Coy in 2003 after he struggled to find a photographer to take his online dating profile pictures, quadrupled in business from 2004 to 2006. With the exception of some recession years, the Oregon-based company has seen steady growth since, snapping photos for more than 15,000 customers.

"Few things are quite as personal - and as scary the first time we do it - as posting our photographs on an online dating site for the entire world to see," Coy said.

Dating photos are different from other types of pictures, Coy insisted. "You only get that split-second chance to make a good first impression on a dating site."