In the case of the Victoria Park incident, the clip posted online showed only Craig Platt, who was subsequently charged with assault, shoulder-charging a teenager, knocking him off his skateboard. He then pushed a man by the throat when confronted about it. It did not, as Mr Platt conceded, "look flash".
As context was supplied to the episode, however, a different picture emerged.
Mr Platt had been helping to judge a competition organised by a drug rehabilitation clinic for under-16 skateboarders. He had become annoyed at teenagers cutting off competitors.
"One of them leapt the rock garden and whacked into a little, tiny kid and just walked away," said Mr Platt. "I asked them several times to stop. I got abused. They kept doing it - interrupting, cutting people off." That was when he decided to act.
Further context was added with time. This appears to have been an incident in which teenagers accustomed to using the skate park became upset when they found a competition thwarting their normal activity.
Their response, according to Mr Platt, was to set him up. That may or may not be so. But history is replete with instances of cameras being used to manipulate sentiment.
There is still debate over whether Robert Capra's 1936 photograph of the death of a Spanish Republican soldier was staged. But not that it became a symbol of that country's Civil War. And debate whether footage showing a 12-year-boy huddling by his father being shot by Israeli forces in Gaza in 2000 was what it said it was. But not that it became a symbol of Palestinian resistance.
It is hardly surprising material that has been set up and is seeking a similar popular response will be posted online. And that people viewing it without any sense of context will simply see what they want to see.
The supply of context may not be enough to reverse their initial response even if they feel inclined to question that.
The simplicity of video-recording and internet posting accentuates the possibilities for justice and, perhaps, injustice.
As evidenced at Victoria Park, the very fact of footage of an incident can be used as a threat. Its power to damn is apparent to everyone. More of its power to mislead needs to be recognised. If internet footage is now the first draft of history, it must be seen for what it is, revealing but unrefined.