Martin Luther King digital archive opens to public
The King Center has published 200,000 personal documents belonging to Martin Luther King Jr, as the US marks the civil rights leader's birthday.
US President Barack Obama and his family marked the day volunteering at a library in Washington DC.
King's memorial is open to the public for the first holiday since it opened.
The documents, which had been kept at the King Center in Atlanta, include scraps of paper with sermons and letters written from prison, as well as hate mail addressed to King, calling African-Americans "savages".
Martin Luther King III, president of the King Center, said the archive "is helping to preserve and extend my father's important message to sustain the momentum of non-violent social change around the world".
Speaking from the library of a Washington school, Mr Obama said: "There's nobody who can't serve," adding that participating in community service was the best way to celebrate the civil rights leader's legacy.
The president and his wife helped the school erect bookshelves and the president painted King's quote: "The time is always right to do what is right," on the library walls, while First Lady Michelle Obama painted "I have a dream".
Meanwhile, civil rights workers and federal officials laid wreaths at the Martin Luther King Jr memorial, on Washington's National Mall.
The memorial, which only opened last summer, has been enveloped in controversy since its unveiling. An incorrect quotation inscribed in its side is to be replaced, it was reported late last week, after complaints that it misrepresented King's words and deeds.