Since the Vancouver Police Department asked the public to send in riot photos, the force has received hundreds of images depicting the mayhem. Now it just has to figure out which of them are real.
Social media have, in some ways, been a blessing for riot investigators, providing evidence that otherwise might never have seen the light of day. But it could also prove to be a curse, with police confirming they're aware that images could be digitally altered, and social-media experts predicting the "That picture was photoshopped!" defence will be popular.
Dave Teixeira, who owns a communications firm, launched canucksriot2011.com shortly after the Stanley Cup melee that left more than 100 people injured and caused millions of dollars in damages. The website, like several others that popped up overnight, features images of the rioters and invites the public to identify them.
Mr. Teixeira himself has sent a couple of dozen e-mails to police - it's anyone's guess how many others have been forwarded by those visiting his site. But along with the genuine photos of young men and women smashing windows and looting stores have been doctored images.
"I have received everything from clearly photoshopped [pictures]to ones where I can't tell," he said.
Some of the obviously edited images show rioters in Montreal or London. In one picture, a man has crudely been pasted in front of the flames on what appears to be a Vancouver street.
But for some photos, it's much more difficult to confirm the authenticity. One image on canucksriot2011.com is titled "Hipster Moron Destroying Police Car" and shows what appears to be a young man jumping. The image appears lit up at different points and has a slight blurring effect, which could indicate it's been altered.
"Hmmm… again, this sorta looks photo-shopped. The colours and the contrasts just don't look right somehow. I could be wrong …" one of the website's visitors posted. Mr. Teixeira replied that the photo came from a reputable source.
Constable Jana McGuinness, a Vancouver police spokeswoman, wouldn't confirm how many doctored images police have received, but said investigators are aware of the possibility of fraud.
"We have experts assisting the investigation that will validate the authenticity of all photographs and images that will be entered as evidence in future court proceedings," she wrote in a statement.
Exactly why someone would alter riot photos remains unclear. Perhaps the image could be used to land a rival in hot water. Or maybe a large number of fakes would undermine the faith of police and prosecutors even in legitimate photos.
Peter Chow-White, a communications professor at Simon Fraser University, said the credibility of riot photos could well come up when cases reach the courts.
"Trying to validate every single one of those photos is going to be a massive task," he said. "Software that you can use to manipulate, to edit, to change images is ubiquitous. … Any savvy lawyer, that's one of the first things they would do, is question the validity or authenticity of the images."
Stuart Poyntz, also a Simon Fraser communications professor, said despite the opinion the public might hold on some of the riot evidence, pictures can lie.
"This is one of the reasons why the explosion of social media creates a whole other set of problems," he said. "Digital photos have shown all of us how easy it is to manipulate photography, [but]there's still this lingering social consensus that photos tell the truth. In this case, they become something that captures or carries a tinge of authenticity that can be manipulated or used in damaging ways."
How can you tell if an image has been digitally altered?
Jeremy Lim, a Vancouver photographer, says there are a number of characteristics to watch out for.
The first is lighting. Mr. Lim, who regularly took to the streets to document the Canucks' playoff run, said the easiest way to tell if the lighting is the same on all subjects is to look at the shadows on their faces. The shadows should fall the same way on people photographed in similar positions.
The second area is depth of field. "If someone's head and body are on the same plane - the same distance from a camera - they should be equally in focus, unless there is motion blur," Mr. Lim said, cautioning there can be variance depending on the equipment and settings used.
Image degradation can also indicate a photo has been manipulated. Edited areas might have more or less pixelation than the rest of the picture, and the colours and contrast could also be off.
Just as MP3s come with metadata that digitally identifies the artist, album and song titles, images come with metadata of their own. Some sites, like Facebook, strip out that information, but Mr. Lim says if an image has been taken with a mobile phone or point-and-shoot camera there's little reason for it to have passed through editing software unless it's been altered.