We only respond if there's video.

That's one lesson that can be drawn from the belated reaction to football player Ray Rice knocking out his fiancee in an elevator. Rice was arrested back in February, and in July was suspended for two games. But once video of the actual punch surfaced this week, he was banned indefinitely.

Time and again, we are informed of outrages — Rice's domestic violence; beheadings and rape by the fanatics calling themselves the Islamic State; Donald Sterling's racism; abuse of prisoners at Abu Ghraib — but only grow outraged and force action when video or audio or images emerge.

How many injustices get short shrift because nobody's recorder was rolling?

"It's frustrating," said Valenda Campbell, who is in charge of creating video and photo images for CARE, one of the world's largest humanitarian organizations.

Campbell and her colleagues at Atlanta-based CARE call it the "CNN effect": when TV cameras arrive at a crisis, donations start pouring in.

"We have a responsibility to help one another. Every day we see these emergencies, and nobody seems to be aware of them," said Campbell, whose organization is now responding to humanitarian crises in South Sudan, Syria, the Central African Republic and Gaza.

She has learned to work within this reality. Her job as senior manager for marketing and creative services is to document images of disaster and injustice — and the healing that follows — which help generate the funds CARE needs to provide assistance.

"It always goes back to the old adage that seeing is believing," Campbell said.

"We are visual beings, and more and more this is a visual culture," she continued. "Seeing things provides more information and puts a human face on whatever the situation is, and helps people relate on a much more personal level to what's going on."

In the Rice case, video was released Feb. 19 of the Baltimore Ravens running back dragging his unconscious fiancee, Janay Palmer, out of a casino elevator, after what police described as an altercation.

Rice, who married Palmer the following month, was charged with assault, which carried a penalty of up to five years behind bars. Charges were later dropped when Rice entered a pretrial intervention program. The NFL suspended him for two games, there was widespread criticism of the penalty as too light — and we moved on.

Then TMZ.com released video from inside the elevator, of the knockout punch itself. There was an enormous uproar. The NFL suspended Rice and the Baltimore Ravens cut him from the team. Many predict he may never play in the NFL again.

"We saw video, and then we demanded justice," sports broadcaster Dan Patrick said on his program.

"Until you have that video, it's 'Oh, really, that happened?'" Patrick said.

A similar dynamic was recently evident concerning the Islamic State group, whose crimes were well documented yet provoked little international action until two videos were released of American journalists being decapitated. On Wednesday, President Barack Obama announced a military response that includes U.S. missile strikes and ground troops from other nations.

"It is very, very scary that we could go to war over two videos," said Robert Thompson, a professor of popular culture at Syracuse University.

"Words are abstractions, and pictures are a presentation of the thing itself," he said. "On some level, we are probably wired to be much more responsive to something we see."

Which can be a good thing, Thompson said, citing images that turned the course of America's involvement in the Vietnam War and the 1960s civil rights movement — Vietnam photos of an execution and a fleeing girl, her clothes burnt off by napalm, or film of African-American protesters being battered by fire hoses and bitten by dogs.

There are stories that command attention without sensational video, such as Edward Snowden's leaked documents. There is national outrage over the killing of Michael Brown in Ferguson, Missouri, though there is no video of the fatal shots. And when there is video, it can be interpreted in different ways, such as the Rodney King police beating tape.

But television is the most popular way people get their news, followed by computers, according to a 2014 study by the Media Insight Project. On television, news can be elevated or ignored depending on how "dramatic" the video is — regardless of whether or not the news itself is important. The exploding online culture, with its insatiable thirst for clicks, has magnified the value placed on images that hit an emotional nerve.

The Rice video was in some ways "the smoking gun," said Todd Boyd, a scholar of popular culture at the USC School of Cinematic Arts.

Before the recording emerged of Los Angeles Clippers owner Donald Sterling making racist remarks, Boyd had been blogging for 10 years about widely reported evidence of Sterling's racist behavior in his real estate business. Sterling settled a housing discrimination case with the government, but few protests were raised until the recording came out.

"A lot of these recordings, Donald Sterling, Ray Rice, in some ways it's like evidence in a courtroom," Boyd said

"As citizens, we're in the digital age now so things are different. In previous generations, we didn't necessarily have access to this type of private information. Now there is so much available to the public, and we treat it like evidence."

He said that people now expect to see some sort of evidence connected to a news story.

"This has become part of the experience," Boyd said. "Where's the tape?"

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National Writer Jesse Washington: www.twitter.com/jessewashington