NEW YORK -- It's becoming clearer and clearer that smartphones have ushered in a new era of police accountability. Since mid-July, when a bystander on Staten Island filmed the death of Eric Garner in a prohibited police chokehold, at least eight other unsettling videos, most of them captured by smartphone, have emerged showing instances of apparent excessive force by NYPD officers. Four such videos have appeared this month alone.

Although police might intimidate bystanders into thinking otherwise, it's perfectly legal to film the cops -- not only in New York, but everywhere in the U.S. -- as long as you don't get in their way. Donna Lieberman, executive director of the New York Civil Liberties Union, encourages people to keep using their phones to film troubling police incidents. The more people who post these videos online, she said, the more likely it is that other people will reach for their own phones when they see cops doing something questionable.

"When police wrongdoing is captured on videotape, it makes the public understand what has happened and why we need to hold the police accountable, and that we need changes in the way police do business," Lieberman told The Huffington Post.

"Nobody would have believed what happened to Rodney King if it hadn't been caught on videotape," she added, referring to the man who was brutally beaten by Los Angeles cops in 1991, leading to months of protests. "The same is true for Eric Garner."

Lieberman also argued that the modern-day proliferation of video is actually good news for police officers.

"It's ready-made training material, and sometimes it's a ready-made defense against wrongful accusation," she said. "It should protect good cops and hold accountable those cops who fundamentally disrespect the rights and laws they're supposed to protect."

On July 17, NYPD officer Daniel Pantaleo put Garner, a father of six and grandfather of two, in a chokehold during an arrest for selling untaxed cigarettes on a Staten Island sidewalk. Bystander Ramsey Orta filmed the arrest. The video shows Garner, who had asthma, repeatedly screaming "I can't breathe!" before his body goes limp.

"Twenty years ago, Ernest Sayon, right in that same district, died," the Rev. Al Sharpton later said at Garner's funeral, referring to another Staten Island man who died at the hands of the NYPD in 1994. "We marched then. But there's a difference this time. This time, there was a video!"

That video, and the others that have emerged since, have raised serious questions about what's going on at the NYPD -- such as:

Why are officers still using chokeholds to apprehend suspects, even though the maneuver is prohibited by the NYPD patrol guide?

On July 14, Ronald Johns, 22, allegedly entered a New York subway station without paying a fare. When he resisted arrest, cops pepper-sprayed him and put him in a chokehold:

Chokeholds are dangerous and often deadly, yet from 2009 to 2013, the city's Civilian Complaint Review Board received more than 1,000 complaints about them. Below is a video, also from July, that shows an officer appearing to put Rosan Miller in a chokehold during an arrest for illegally grilling outside her home in East New York, Brooklyn. Miller, 27, was seven months pregnant at the time.

Which leads to another question: How are officers trained to deal with pregnant women, anyway?

Here's a cop slamming visibly pregnant Sandra Amezquita to the ground.

This video is from mid-September, when Amezquita tried to intervene in the arrest of her son outside a restaurant in Sunset Park, Brooklyn. She alleges that officers also beat her belly with a baton.

The NYPD didn't respond to a request for comment from The Huffington Post about how officers are told to treat pregnant women. A copy of the department's patrol guide says that "when possible," electric devices like a Taser "should not be used on children, the elderly, obviously pregnant females, the frail, [or] against subjects operating or riding on any moving device or vehicle." The guide also tells officers, "If possible, avoid using pepper spray on persons who appear to be in frail health, young children, women believed to be pregnant, or persons with known respiratory conditions."

Also in September, and also in Sunset Park, police officers threw fruit vendor Jonathan Daza, 22, to the ground after reportedly telling him to pack up his table and clear the area. Once Daza was on the ground, Officer Vincent Ciardiello kicked him in the back, apparently without provocation. Ciardiello was later suspended.

Daza's encounter is just one recent example of New York police appearing to use excessive force on young men of color, a pattern that has led community leaders to ask, repeatedly: Are cops unfairly targeting young black and Latino men for petty crimes? (Statistics certainly suggest that they are.) Below is a video of 17-year-old Marcel Hamer allegedly getting punched unconscious by a cop in Clinton Hill, Brooklyn.

According to Marcel's lawyers, the incident took place in June. The cop had accused Marcel of smoking marijuana, though Marcel's attorneys maintain that it was only a cigarette.

Below is footage of a cop in Brooklyn's Bedford-Stuyvesant neighborhood appearing to hit 16-year-old marijuana suspect Kahreem Tribble in the face with a gun. Before the cop hits him, Kahreem can be seen with his arms raised in surrender.

There is also video of 23-year-old Santiago Hernandez apparently getting beaten by a group of officers in the Bronx, an incident that reportedly happened in mid-August.

So despite all these videos, and despite the NYPD reminding its officers this summer, why do some cops still not know that it's perfectly legal to film police behavior?

The video above shows an NYPD school safety officer breaking the camera of an NY1 reporter who had been trying to interview students. (It should be noted that when a different group of cops got to the scene, they informed the safety officers that the NY1 crew was within its rights to film police and to interview students on a public sidewalk.)

The NYCLU has a "Stop and Frisk Watch" app that you can download here, though Lieberman cautioned that anyone who tries to film police activity is taking a risk.

"It's important that they not insinuate themselves into what's going on," she said. "You can film, but you can't interfere with police activities. I think that people have to be discreet, because there are many officers still who don't understand their obligation to respect the rights of the public to take pictures."