On Oct. 6, the oldest Columbus Day parade in the country, in downtown Denver, had its 100th anniversary. Native Americans have for years protested the event, pointing out that Christopher Columbus pointed the way for four centuries of genocide in the New World. This year's parade quickly descended into shouting matches between the Indians and the Italian-Americans trying to celebrate their heritage -- all of it captured in a series of images by photographer A.J. Schroetlin, now posted on his Flickr page.

What has this to do with the Web 2.0 Summit, getting under way tomorrow in San Francisco? Well, for one thing, Flickr co-founder Stewart Butterfield is hosting a "Show Me" session at the conference, on Friday afternoon. Beyond that, as Summit co-chair Tim O'Reilly told me when we had a preview chat yesterday, one of the "subterranean threads" running through the brainstorming sessions over the next three days is a constellation of ideas orbiting around the central notion of Web 2.0 as a locus of collective intelligence, often based on sensors or images as much as blogs and "people typing away on keyboards," said O'Reilly.

"Most people see Flickr as a photo-sharing site, but in some ways it's becoming the eyes of the global network," he added. "These Web 2.0 apps are getting eyes."

The Denver Police were forced to defend their actions at the Columbus Day parade after 83 protesters were arrested and many of them alleged excessive force on the part of the officers. Schroetlin's images don't include any out-and-out examples of police brutality, but they do show some pretty scary shots of rather zealous enforcement, like this and this.

These are less egregious examples of the sort of procedure we saw with the now-famous "Don't tase me, bro!" video on YouTube of a University of Florida student manhandled and tased by several peace officers (which, by the way, now has several entertaining remixes, songs, and other related mashups along with the original footage).

So, I will ask Stewart Butterfield: Are Flickr and YouTube and other image/video-based Web 2.0 apps going to become a sort of reverse-field surveillance mechanism, by which the disempowered capture (and, more important, display for a global audience) the actions of the powerful? The answer seems pretty obvious. The implications, not yet so.