Historical Photographs of China is an online collection of digitized images of pictures taken between 1870 and 1950. Its 6,000-plus images can be searched by keyword, date, and so on. The collection's designers are continuing to expand it and are seeking feedback from users.
Below are free digital libraries and archives covering images, photographs, prints, newspapers, manuscripts and archives about China or Chinese culture.
China: Trade, Politics and Culture, 1793-1980: Provided through Adam Matthew Digital, ideal for any independent project covering almost every aspect of Chinese history, you can find primary sources such as unpublished manuscripts, letters, prints, photographs and maps from 1793 to 1980. (Available ONLY through NYU)
For more images, check out NYU's databases