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."

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.

Senior Dogs Across America

14-year-old Curley from Kanab, Utah

Senior Dogs Across America

16-year-old Joon from Sandwich, Mass.

Senior Dogs Across America

18-year-old Rex from Seattle, Wash.

Senior Dogs Across America

19-year-old Champ from Butte County, South Dakota

Senior Dogs Across America

21-year-old Breebee and 19-year-old Nuny from Ralston, Wyo.

Senior Dogs Across America

17-year-old Springfeather from Kanab, Utah

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