Early invention of photography?

It seems to me that all the prerequisites for the invention of photography were there as early as the 1600s. Could an early Enlightenment-era scholar have developed the art of photography in this period, and could the technology have become widespread by 1700? If so, how would that have changed the world? I know that Matthew Brady's battlefield photos produced a substantial amount of anti-war sentiment during the American Civil War - could earlier battle photographs have done the same for the War of the Spanish Succession, or photos of slave ships have energized the early Abolitionist movement? In the field of art, would we see earlier movements away from representational art, now that the camera is competing with the painter?

On a related note, how soon could color photographs become widespread? OTL, the first color photo was made in 1869 by Maxwell, and by the turn of the century, we had these amazing photos:

http://www.loc.gov/exhibits/empire/

But color photography didn't become the standard until the 1960s. Did economic considerations make this inevitable, or could we, if things had gone a little differently, be looking at color photos of the War of 1812 today?
 
Though this is less plausible, a photographic process could have been invented in Song Dynasty China - the pinhole camera was known, and if a Daoist alchemist had made a lucky discovery and put two and two together... I don't even know how to start extrapolating from the invention of photography in, say, 1100 in China.
 
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