Blowtorches, tweezers and glue: These are just a few of the items used to create those mouth-watering restaurant ads. To make food look as appealing as possible, food stylists and photographers use a range of instruments, good lighting, fresh ingredients and attention to detail. These tricks of the trade help explain why restaurant meals from the drive-thru often look very different than they do in promotional images.

Some of the tools that a food stylist would use during a photo shoot Source: Bybee Photography Inc.

"Nothing is just plopped down and put in the center like it is when you order at a restaurant," said Jean Ann Bybee, owner of Bybee Photography and co-author of a pair of books about food styling.

During shoots, stylists use tweezers, toothpicks, scissors, small blowtorches, paper, tape, glue, pins, paint, oil and glycerin to manipulate and enhance food, Bybee said. To see the differences for ourselves, CNBC hit the pavement, ordered items from a range of restaurants and compared orders with promotional images below.

Dunkin' Donuts Eggs Benedict sandwich (Left: promotional image; Right: CNBC's order) Source: Dunkin Donuts (L) | CNBC (R)

Often, the food in the photos isn't even fully cooked. "Let's say we're shooting a beef burger. It may not be cooked all the way through because we want to maintain the size of the burger," said Janine Kalesis, a food stylist who has worked with Chipotle Mexican Grill and Kraft's Velveeta. Once cooked, meat and vegetables tend to shrink, and vegetables begin to wilt.

Burger King's Big Fish sandwich. Source: Burger King (L) | CNBC (R)

"Mainly the reason why we're not cooking things all the way through is it's sitting on set," Kalesis said. "It can sit on set for up to an hour before we have the final shot." For restaurant photo shoots, stylists say restaurants supply the food and emphasize maintaining their recipes. "Companies are so concerned today with overpromising and portion control, so we really have to work with their guidelines," said Nir Adar, a New York-based stylist whose clients have included Chick-fil-A, Yum Brands' Kentucky Fried Chicken, Burger King and White Castle.

Starbuck's bacon gouda artisan sandwich (Left: promotional image; Right: CNBC's order) Source: Starbucks (L) | CNBC (R)

While working with Burger King, Adar said he's even had to sign a legal document saying he didn't alter anything. Chick-fil-A demanded that he use its procedures. "Most companies today want it to be fresh, natural, not overworked," Adar said. McDonald's, Burger King, Starbucks, Chipotle and Yum Brands didn't respond to CNBC email requests for comment about the practice of food styling. A Chick-fil-A spokeswoman said the company isn't sure it would "be a fit for this story" since it takes a different approach to using food in its commercials, which often center on cows advising people to 'eat mor chikin.'

A Wendy's spokesman said about food stylists, "We supply the same ingredients to them as our restaurants receive. We also require that they prepare and build the products to operational procedures. The big difference is how much time we take to get an appealing shot." In a statement, Dunkin' Donuts Spokeswoman Michelle King said, "Dunkin' Donuts always uses real Dunkin' Donuts product in our advertisements. Our shoot director and food stylist team build the products to the exact specifications provided by Dunkin' Donuts' chefs to match what will be sold in our restaurants. We strive to ensure the authenticity of our products in our advertising." On the regulatory side, Federal Trade Commission spokeswoman Betsy Lordan told CNBC by email that truth in advertising laws do apply to restaurant menu items displayed in ads. The commission examines both what's implied by and stated in an ad to determine whether it's deceptive. "There are no specific FTC regulations governing food photos used in advertising, and the FTC has not pursued any cases alleging that food ads are deceptive based only on the photos," she wrote. If, for example, customers see that McDonald's fries look different in person than in an ad, that would not cause the same regulatory concern as a false claim that a product has special properties, like reducing the risk of illness.

Wendy's Tuscan Chicken on ciabatta sandwich (left: promotional image; right: CNBC's order) Source: Wendy's (L) | CNBC (R)

"Consumers frequently purchase food, it's relatively inexpensive, and it's fairly easy for a consumer—without any specialized training—to evaluate whether the food they get looks enough like the food in the picture to justify purchasing it again," she said. To satisfy curious diners, one fast-food giant has even lifted the veil on a photo shoot. In a 2012 video, McDonald's Canada attempted to answer the question, "Why does your food look different in the advertising than what is in the store?"