The Massachusetts Bay Transportation Authority is investigating cases of people cheating the system and riding the T for free, and all of it caught on camera.

MBTA Transit police said at least 90 people were using discounted Charlie Card passes meant for blind riders. The passes allowed people to hop on the T for free for five years.

The problem was, they could see just fine.

A keen-eyed transit patrolman allegedly caught one rider with a bogus pass, breaking the case open.

The investigation led detectives to a former MBTA temp worker who allegedly sold the passes to people for about $50. Detectives said they plan to charge Giovanni Francis, 19, of Hyde Park, in connection with selling the cards.

Investigators said Francis is also suspected of stealing and then reselling senior citizen MBTA fare cards on CraigsList.org. However, he has not yet been charged.

All of the illegal cards have now been deactivated.

The passes were being used illegally at the reduced fare aisles at MBTA stops throughout the state, including the Prudential, Riverside, and JFK stops. Had the theft not been thwarted when it was, the cost to the MBTA could have topped $500,000.

MBTA police shared surveillance pictures captured from several different stops exclusively with Team 5 Investigates' Sean Kelly. One shows a woman smiling as she walked through the turnstile for free. Another shows a mom with several children using an illegal card.

"I think what's most disheartening about this thing is that I can't think of anything more despicable than people who are actually stealing passes from blind people," said MBTA general manager Dan Grabauskas.

All 90 illegal cards were processed at the MBTA Center at Downtown Crossing, where Francis worked.

Authorities said anyone who bought one of these illegal cards can turn it into transit police without prosecution if they cooperate and tell transit police how they got it.