I’ve long noticed that on Flickr, the comments all seem to be predominantly very polite and positive. People tend not to post anything rather than post something negative.
I’ve especially noticed this on pics of t-girls. Even when, to be brutally honest, they don’t actually look very good (to the extent it’s clearly a guy who has pulled on one of his wife’s dresses and plonked a wig on his head) people feel the need to build them up with gushing praise about how fantastic they look.
However, the corollary to this is that people then tend to get an artificially positive feeling about their pics and I’m not sure that’s particularly productive.
It also throws doubt onto all of the positive comments on my own Flickr.