As photographer Nancy LeVine watched her dogs Lulu and Maxie approach their final days, she was inspired to immortalize them and other aging dogs.

The project became an eight-year, cross-country endeavor known as "Senior Dogs Across America," including a book featuring 86 of her best portraits.

LeVine says she was interested in capturing senior dogs because of what their aging means to the people who love them and because of how differently man and man’s best friend age.

"The dog lives in the present,” she told the New York Times. "We don't. Our body is fragile. We're thinking about the past and what we could have done differently; we’re thinking about the future and what is going to happen to us."

LeVine has photographed numerous elderly dogs over the years. Some of her subjects live in sanctuaries, while others are spending their long lives with the families that adopted them as puppies.

Most of the dogs she photographs are more than 15 years old, but LeVine says she makes exceptions for larger breeds, which often don’t live as long.

Although she captures images of canines in their final days, LeVine says "Senior Dogs Across America" isn't about the dogs' deaths, but the dignity of their aging.

"I saw how the dog does it; how, without the human's painful ability to project ahead and fear the inevitable, the dog simply wakes to each day as a new step in the journey," she writes in her artist statement. "Though their steps might be more stiff and arduous, these dogs still moved through each day as themselves."

Take a look at some of LeVine's touching photos below and find more on her website.

Senior Dogs Across America, Curley from Utah 14-year-old Curley from Kanab, Utah

Senior Dogs Across America, Joon from Sandwich 16-year-old Joon from Sandwich, Massachusetts

Senior Dogs Across America, Rex from Seattle 18-year-old Rex from Seattle, Washington

Senior Dogs Across America 19-year-old Champ from Butte County, South Dakota

Senior Dogs Across America, Breebee and Nuny from Wyoming 21-year-old Breebee and 19-year-old Nuny from Ralston, Wyoming.

Senior Dogs Across America, Springfeather from Kanab, Utah 17-year-old Springfeather from Kanab, Utah

Laura Moss writes about a variety of topics with a focus on animals, science, language and culture. But she mostly writes about cats.

Dogs age with dignity in photographer's work
Nancy LeVine travels the country immortalizing elderly canines as part of her 'Senior Dogs Across America' project.