Painting, photgraphy and the role of different media
From Renaissance (when artists started to pay attention to anatomy and discovered perspective) to the late 19th century, art was always, more or less, realistic. Many people believe that until the advent of Impressionism, the role of art was solely reproducing the world as it is seen. It is not, however, exactly true.
While the art of Renaissance seems to be realistic, it was, in fact, made according to mathematical proportions regarded as perfect by Greco-Roman philosophy.The real subject was, then, painted as it is, however, "improved". It was, still, a possible reality, just perfect.
Some later artists, as (for example) Caravaggio and Vermeer, are often regarded as "photographic". They did not follow "perfect" proportions, neither portrayed idealized subjects. Many were known to use devices as the camera obscura and the camera lucida, that projected the image onto a surface, the only difference between photography being the need of the hand of the artist to draw the projected image.
With the advent of the daguerreotype (the first permanent form of photography) in the 1840's, painters feared losing their means of living. It could register the forms of the objects perfectly, objectively, without interference of the artist, and altough it lacked color, it could be colored by hand, far more cheaply. It is even taught that Impressionism, and later less realistic styles of art, were developed as a means of keeping painting alive. It is, however, not true. Proof of this is the vast amount of realistic and academic art produced in the late 19t/early 20th century, accepted by society, while other forms of art were considered extravagant, shocking and even immoral. The reason why Impressionism and later developments are taught and its contemporary traditional art remains despised and even unknown is because it shaped what would be the mainstream 20th century art. Artists like Bouguereau, Alma-Tadema, Tissot and Sargent are worth mentioning, the later having incorporated aspects of Impressionism in his paintings.
In fact, painting, as opposed to photography, is capable of registering not only the texture and brushstrokes of the artist, but the quality of line (rough or fine), shape, surface (smooth and simplified or highly detailed) the artist intend to represent, emphasizing the aspects of the subject he wishes to portray to express his ideas and impressions. The same subject can be represented in entirely different ways by different artists. Photography is only partially capable of it, through the quality of light, film, and focus.
Present and future
With the advent of digital painting, photography and editing, the line that divides these two media became even more blurry.
A photograph can be easily edited, the colors and contrasts changed, the focus adjusted and the exposition altered, to make it portray what the artist want to express. Yet, it lacks the spontainety, the brushwork and the quality of line the hand of the artist can produce.
There is another aspect that cannot be properly controlled: texture. Altough prints can be made into textured material, it cannot properly mimic the quality of every material. Oil paint, for example, depending on how it is prepared by the artist (or by the manufacturer) can offer unique depht, vibrance and gloss.
Painting and photography, however blurred, will always be different media suited for different purposes.