– A Miami felon nicknamed “Crazy Goat” got cuffed on a weapons rap after posting photos of himself loading guns.

Months later, online snapshots helped police pin charges against three teenagers on allegations of drug-fueled group sex with underage girls.

Then there was a petite teen named Karla Sanchez who saw a naked overweight woman in the shower of a North Miami gym. She whipped out her smartphone, snapped a photo and immediately posted it. Her not-so-smart caption: “The things I see at LA Fitness. WTH!”

Within weeks, cops jailed Sanchez, 18, on a misdemeanor voyeurism charge.

Each of these recent cases stemmed from photos or video posted on Instagram, the fast-growing social media site that has increasingly become a treasure trove of evidence for police and prosecutors.

Several weeks ago, Miami-Dade detectives sent search warrants to Instagram’s corporate office, hoping to obtain posts to seal convictions for two defendants awaiting trial, one of them for murder.

“We encourage the criminals to post their photos and videos online,” said Miami-Dade State Attorney Katherine Fernandez Rundle. “After all these years, they’re still kind enough to do it.”

Spilling the beans on social media has become so common that defense attorney David Seltzer, a former Miami-Dade cybercrimes prosecutor, now makes it a point to caution his clients.

“I think technology has made people relaxed and made people let their guard down,” Seltzer said. “First thing I tell clients is, ‘Turn off your social media. Why make the job of the police easier?’ ”

There have been a number of notable social-media crime cases, topped by Derick Medina of South Miami. In 2013, he shot his wife and then uploaded a photo of her dead body and a confession to his Facebook page. Medina, who is awaiting trial, claims self-defense.

Founded in 2010, Instagram has boomed, becoming so big that Facebook paid $1 billion to buy the company that an industry analyst recently valued at $35 billion. Last month, Facebook announced that 300 million people use Instagram each month.

Alex Jordan, a Dartmouth University psychology professor who researches social media habits, says Instagram helps people “advertise a heavily filtered and more-interesting-than-reality image of themselves and their lives.”

“Instagram can feed our narcissism, or at least reflect it,” Jordan said. “All it takes is a bit of overconfidence to lose sight of the legal and personal risks of posting potentially incriminating photos or other information online.”

In November 2013, serial shoplifter Leroy Minnis stole $2,238 worth of merchandise from the Hollister store at a mall in South Miami.

To sell the shirts, Minnis posted photos of them on his Instagram account, “WhoisPuti.” Another photo, with one woman on each arm, also showed him wearing a black T-shirt with gold lettering — the same one seen on store surveillance video.

He’s now serving a 32-month prison sentence.