During a lunch date with with girlfriend and Glee costar Lea Michele, troubled actor Cory Monteith brazenly showed off what appears to be injection marks on his arm -- TWELVE months before his death.

Photos reveal the actor, who died on July 13 of a lethal mixed drug toxicity of heroin and alcohol, with possible injection sites on his arm in Los Angeles on July 9, 2012.

A month later, Monteith was snapped in Soho, New York, with similar markings.

The fact that Monteith had a number of "track marks" on his body would have made it clear to anyone around him that he had a drug problem.

According to reports, the actor was encouraged to get help by the Glee cast and crew in early 2013, when it became apparent he was battling addiction.

Friends, including Michele, 26, convinced him to enter rehab in April, though it's said his girlfriend "didn't know" that he had relapsed with heroin following what was to become his second stint in treatment.