Guys who feel like masturbating, flashing, or groping people on the subway better think twice unless they want to get caught and charged with a crime. Thanks to cell phone cameras, it’s easier than ever for people to snap photos of perpetrators and report the crimes.

HollaBack NYC has long advocated for the use of cell phone pictures to shame harassers and report those who cross the line to criminal activity. In fact, the idea for the blog was born after a woman in NYC used her cell phone to snap a picture of a subway masturbator and report him.

[Update: If you’re in the Astoria area of NYC, look out for this alleged subway sexual assaulter and if you see him, contact the police. The woman snapped his picture and has reported him]

A few months ago in Washington, D.C., a photo of a metro station upskirter and groper posted on HollaBack DC! helped lead to his arrest.

And now in Boston, CNN reports that a MBTA rider’s cell phone picture posted on Twitter led to the arrest of a subway flasher.

“Rider Nay Khun was riding the train Wednesday afternoon when he spotted the suspect ‘fidgeting with his crotch area with his zipper open and his penis exposed,’ according to the MBTA.

Khun immediately posted to his Twitter account a photo of the man, saying ‘pervert on the 2nd car of the red line … help me report him.’

The man is a known offender, MBTA police told CNN affiliate WHDH.

He was arrested Friday for open and gross lewdness, according to a statement from MBTA police.”

Nice work Khun and a big thank you to the Boston transit authority and police for taking this issue seriously.

No matter where you live, if you can, take pictures of harassers and post them online. If they grope, stalk, threaten, or masturbate at you, report them! Let’s use technology to our advantage and put these creeps on notice. They should know there will be consequences for their actions.

(Thanks Violet Kittappa, Director of Research and Development for Hollaback NYC, for the CNN story tip)