A close-up black and white image of the late actor with the caption 'The hardest word to say is "goodbye' was released by the TV show's screenwriter Ryan Thomas on Twitter.
The final episode, which Cory's girlfriend and co-star Lea Michele is helping to write, will air on 10 October.
The show will remember Cory's character Finn Hudson and deal with the subject of drug abuse.
Lea recently tweeted a picture from the set of Glee of her wearing a necklace that paid tribute to Cory's character Finn while they were filming the special episode.
The show will start off with the news that Finn has died, and follow through with the characters remembering and honouring him. Lea is not expected to appear until the end of the episode.
"Just read Cory Monteith memorial episode," tweeted Jane Lynch, who plays sports coach Sue Sylvester in the show, earlier this week. "Most beautiful thing. Thank you, @MrRPMurphy @BFalchuk Ian Brennan."
The cast of Glee have been working hard to support and comfort each other, and Lea is said to be doing an "amazing" job at holding her co-stars together.
"Lea has been amazing," a source told HollywoodLife. "She is definitely very sad, but has gotten so much better and has really been strong.
"The whole crew and cast are now a family and Lea is leading us all back to a normal set life. Cory was a cool guy and will be missed."
The show's leading lady has been letting fans into her Glee world and thanking them for their love and support following Cory's death from a heroin and alcohol overdose in mid-July.
She has also kept fans in the loop by sharing photos from the set of the hit musical show.
The cast have been working hard to support and comfort each other after Cory's untimely death from a heroin and and alcohol overdose in mid-July.
The fifth season of Glee will premiere in the US on 26 September and will end with the special memorial episode for Cory on 10 October.