Max Kosloff in his Critical reflections - photographic criticism in American SuburbX makes two points. The first is that photos witness events, with its implication of documentary as opposed to trace:

my criticism was gradually drawn to the contrast between the photograph's nominal and effective content (in Roland Barthes' terms, studium and punctum). The former is usually indicated by the image's social or technical idiom, and the latter is brought out by a wild power to shock, disturb, or touch a viewer, sometimes constructed by artistic design, but more often generated through a fortuitous or maybe inadvertent detail captured within the picture's socialized program. Barthes has written of the detail as a feature that he detaches from the pictorial field through his unsharable private subjectivity. Not only is this ungenerous, it's mistaken, because the unaffecting genre material and the moving detail are indivisible. Photographic images are haunted by the sheer doggedness of the random. I suspect that this is another way of saying that the world has its unpredictable way with them. The world is strewn with obscure, uncalled-for particulars, which mingle indifferently with our programs and our stories. But as photographs blend these particulars in spasmodic ratios, miscellaneous jolts and narrative import are all part of the picture.

The second is that:

The idea that texts are somehow superior to images (as if they could be ranked) sounds crazy to me, but this idea is widely assumed - and goes unquestioned - in academia. In the sociology of higher learning, those who study the visual arts are placed on the bottom rung of an intellectual hierarchy. Literary critics, semioticians, and political scientists, role models all, may be asked to lecture to art historians, but not the other way around. Wishing to improve their status and to blend in, those in the image line could distance themselves from visual objects in their increasingly theoretical work. It says a lot about their approach to the image that they canonized Duchamp, more renowned than any other twentieth-century artist for his animus toward the visual. It says even more that they stamped out pictorial allusions and therefore descriptive appeal from their language, one reason for the abstract tenor of their writing. Suitably deadened in tone, it gained prestige in the semantic environment of grad-student seminars.