Photo taken on Oct. 4, 2019 shows Gustave Le Gray's "Brig on the Water" at the exhibition "The Eye of the Sun: Nineteenth-Century Photographs from the National Gallery of Art" in Washington D.C., the United States. The exhibition marks the 180th anniversary of photography's introduction to the world in 1839 and presents some 140 photographs offering an in-depth look at the development of the medium throughout its first 50 years. It will last until Dec. 1. (Xinhua/Liu Jie)

Photo taken on Oct. 4, 2019 shows Charles Marville's "Cloud Study over the Pantheon, Paris" at the exhibition "The Eye of the Sun: Nineteenth-Century Photographs from the National Gallery of Art" in Washington D.C., the United States. The exhibition marks the 180th anniversary of photography's introduction to the world in 1839 and presents some 140 photographs offering an in-depth look at the development of the medium throughout its first 50 years. It will last until Dec. 1. (Xinhua/Liu Jie)

Photo taken on Oct. 4, 2019 shows artworks at the exhibition "The Eye of the Sun: Nineteenth-Century Photographs from the National Gallery of Art" in Washington D.C., the United States. The exhibition marks the 180th anniversary of photography's introduction to the world in 1839 and presents some 140 photographs offering an in-depth look at the development of the medium throughout its first 50 years. It will last until Dec. 1. (Xinhua/Liu Jie)

A man visits the exhibition "The Eye of the Sun: Nineteenth-Century Photographs from the National Gallery of Art" in Washington D.C., the United States, on Oct. 4, 2019. The exhibition marks the 180th anniversary of photography's introduction to the world in 1839 and presents some 140 photographs offering an in-depth look at the development of the medium throughout its first 50 years. It will last until Dec. 1. (Xinhua/Liu Jie)

A woman visits the exhibition "The Eye of the Sun: Nineteenth-Century Photographs from the National Gallery of Art" in Washington D.C., the United States, on Oct. 4, 2019. The exhibition marks the 180th anniversary of photography's introduction to the world in 1839 and presents some 140 photographs offering an in-depth look at the development of the medium throughout its first 50 years. It will last until Dec. 1. (Xinhua/Liu Jie)

A woman visits the exhibition "The Eye of the Sun: Nineteenth-Century Photographs from the National Gallery of Art" in Washington D.C., the United States, on Oct. 4, 2019. The exhibition marks the 180th anniversary of photography's introduction to the world in 1839 and presents some 140 photographs offering an in-depth look at the development of the medium throughout its first 50 years. It will last until Dec. 1. (Xinhua/Liu Jie)

Photo taken on Oct. 4, 2019 shows William Henry Fox Talbot's "Winter Trees, Reflected in a Pond" (1st R) at the exhibition "The Eye of the Sun: Nineteenth-Century Photographs from the National Gallery of Art" in Washington D.C., the United States. The exhibition marks the 180th anniversary of photography's introduction to the world in 1839 and presents some 140 photographs offering an in-depth look at the development of the medium throughout its first 50 years. It will last until Dec. 1. (Xinhua/Liu Jie)

Photo taken on Oct. 4, 2019 shows photographs at the exhibition "The Eye of the Sun: Nineteenth-Century Photographs from the National Gallery of Art" in Washington D.C., the United States. The exhibition marks the 180th anniversary of photography's introduction to the world in 1839 and presents some 140 photographs offering an in-depth look at the development of the medium throughout its first 50 years. It will last until Dec. 1. (Xinhua/Liu Jie)

Photo taken on Oct. 4, 2019 shows Henry Peach Robinson's "Gossip on the Beach" (L) at the exhibition "The Eye of the Sun: Nineteenth-Century Photographs from the National Gallery of Art" in Washington D.C., the United States. The exhibition marks the 180th anniversary of photography's introduction to the world in 1839 and presents some 140 photographs offering an in-depth look at the development of the medium throughout its first 50 years. It will last until Dec. 1. (Xinhua/Liu Jie)

Photo taken on Oct. 4, 2019 shows Henry Peach Robinson's "She Never Told Her Love" at the exhibition "The Eye of the Sun: Nineteenth-Century Photographs from the National Gallery of Art" in Washington D.C., the United States. The exhibition marks the 180th anniversary of photography's introduction to the world in 1839 and presents some 140 photographs offering an in-depth look at the development of the medium throughout its first 50 years. It will last until Dec. 1. (Xinhua/Liu Jie)