Martin Luther King, Jr., flanked by some of his principal lieutenants: from left to right, Andrew Young, who later became a congressman, ambassador to the United Nations, and mayor of Atlanta; Ralph Abernathy, King’s closest adviser; and John Lewis, who is now a congressman. Photograph by Steve Schapiro.

According to NationalService.gov: Life’s most persistent and urgent question is, “What are you doing for others?” This question was posed by Dr. Martin Luther King, Jr. The organization also states, “On MLK Day, Americans across the country come together for a day of service, picking up the baton handed to us by past generations and carrying forward their efforts. As one people, we show that when ordinary citizens come together to participate in the democracy we love, justice will not be denied. So make the commitment to serve your community throughout the year – and make MLK Day a day on, not a day off.”

People assemble to watch the march pass through Montgomery. This photograph is one of several unpublished images that Schapiro, who covered the third Selma march for Life, recently rediscovered. Photograph by Steve Schapiro.

Years ago, some great photographers captured Americans coming together during difficult times – fighting for the rights of generations to come. Photographers like Steve Schapiro and Gordon Parks whose work is shown here, documented our nation progressing towards a greater equality.

Participants in the march take a break. Photography by Steven Schapiro.

Depicting the march from Selma-to-Montgomery, AL in March 1965, the nonviolent discipline of the marchers became such a resonant chapter in the black freedom struggle that Barack Obama, in 2007, went to Selma to speak in the early years of his Presidency. The march is also the focal point of the Oscar nominated film, Selma.

Mr. and Mrs. Albert Thornton, Mobile, Alabama, 1956. Photography by Gordon Parks.

Untitled, Shady Grove, Alabama, 1956. Photograph by Gordon Parks.

Works by Gordon Parks are currently on display at Atlanta’s High Museum in an exhibit called Gordon Parks: Segregation Story. The exhibit runs through June 7, 2015.