Some movie fans, and even other crew members, might assume that all those promotional images that appear in publications are captured by the lens of the camera shooting the movie. Not true. Those pictures are snapped on set by still photography pros who are members of the Intl. Cinematographers Guild Local 600, also known as ICG Publicists.

One of them is Lacey Terrell whose latest credit is still photographer on the upcoming Tom Hanks film “A Beautiful Day in the Neighborhood,” directed by Marielle Heller (“Can You Ever Forgive Me?”).

“It’s a funky dance we have to do because we’re right at the heart of everything, next to the movie camera and the actors,” says Terrell of her job. “But we are paid to be invisible.”

While these pros have the authority to request that an actor recreate a specific moment, most of the time they’re snapping away while the DP is shooting.

Frank Masi, above left, longtime photographer on the films of Bruce Willis and Dwayne Johnson, above right, considers it the best compliment of all when actors they don’t notice him since remaining out of the eye-line is part of the job.

And, though conditions seem ideal for taking photographs with a professional lighting set-up, it isn’t that simple. “The cinematographer and gaffer are going to light the scene for the A-camera,” Masi says. “And, what looks great lit coming from the A-camera, two feet over does not necessarily look great, because there may be a flare or a shadow now on the actor’s face, and that’s a tremendous challenge.”

But time on the set is fleeting, and capturing a gun flare, emotive expression on an actor’s face or a behind-the-scenes moment means the still photographer must be attentive and aware at every minute.

Part of the job’s balance is in creating art while documenting a specific process, since the photos must reflect what the motion picture camera is shooting. “You don’t want to capture images where you’re shooting at an angle that’s not complimentary to what the film looks like,” Masi says.

And while they may be documenting, still photographers often work with such skill and creativity that their work becomes art in and of itself.

Though the job has been around for as long as motion pictures, the switch to digital from film has presented its own benefits and drawbacks. Technology these days allows photographers to check their images immediately. The drawback: they now they also put in hours of additional work, at times uncompensated, while they sort, organize and upload files.

However, Masi believes the technology favors them. “One of the things you have to do is work really fast and whether that is in the scene composing the shot, getting the shot, finding a way to get in there so you can get that shot — digital allows us to know we got it.” (With film, it could sometimes take weeks to get images from the processing lab.)

“I’m always there, involved and watching how the cameras, operators, dolly grips, and boom operators are moving, while also reading the set and temperament of the actors,” Terrell says. “Much of our job is people skills, while waiting to capture the moment that illustrates our story in one frame.”