This image from Saturday's commemoration of the 50th anniversary of Bloody Sunday captures a moment that instantly became iconic: when the United States' first black president walked hand-in-hand with civl rights heroes whose demands for full equality for African-Americans he knows still haven't been met, even as he spoke to the incredible progress made.

In it, Obama walks alongside Amelia Boynton Robinson, a key organizer of and participant in the march, who's now over 100 years old, Rep. John Lewis, a civil rights activist-turned-congressman, who's said he thought he was going to die on Bloody Sunday, and others who were brutally attacked by police as they attempted to cross the Edmund Pettus Bridge in their march from Selma to Montgomery to demand voting rights for African-Americans, on March 7, 1965.

On Obama's other side, a third generation — his two daughters — are marching, too. They are holding hands with their grandmother, Marian Shields Robinson, and their mom, First Lady Michelle Obama.

This photo is especially moving, as Images from the original Bloody Sunday are hard to come by. This one, from the third leg of the Selma-to-Montgomery march, was taken 3 weeks later on March 22, 1965.

Photos like this, taken during the peak of the civil rights movement, are part of our collective memory of the long fight for racial justice in America.

This weekend's images will join them. Against the backdrop of ongoing battles over voting rights and a newer focus on racialized policing, they're reminders of how far we've come — and haven't — and that, as Obama said in his remarks Saturday, "This is work for all Americans, and not just some. Not just whites. Not just blacks."

Further Reading

Read the full transcript of Obama's rousing, emotional speech in Selma

Obama's speech in Selma was an answer to those who question his love for America

Inside the fight to strip a KKK leader's name from the Edmund Pettus Bridge