We can see some sort of gang, they are all wearing (green?) suits and masks so this might be Riddler's gang from the series finale. Or maybe it's the Mutant gang from 5x03 'Penguin, Our Hero'.

A photo of Penguin from the final episode, he's wearing the purple suit from the 5x12 set photos we got last week.

Above is a good look at Ecco's outfit and her hairstyle.

Right next to it is a photo of ninjas (?) in the shadows, it looks like they've got katana on their backs (League of Shadows? Lady Shiva's army?).

Then there's a photo of Gordon, Penguin and Bruce from 5x11. Oswald is wearing the sunglasses from the promo that will most likely crack during the battle and injure his eye.

A photo of Barbara with closed eyes. Maybe she's dead or unconscious (or I'm reading too much into the photo).

Right below the Bruce picture we can see Barbara, Penguin, Gordon, Tabitha and Bullock at the warehouse where the Wayne helicopter crashed. It seems that Oswald shoots down the helicopter to get the supplies but the GCPD and Barbara also want to get hold of them. It's from 5x01 'Year Zero'.

Also at the warehouse, we can see Oswald holding Barbara at gunpoint. She's kneeling down in front of him and is holding her shoulder, maybe she's injured.

Right below it is a photo of Jessica Lucas and Erin Richards, there is a table with cake on it. It looks like Jessica Lucas just filmed her last Gotham scene and the cast is there to celebrate with her. I once heard in an interview that the Gotham cast and crew throw a party for an actor when he wraps his final scene on the show, so this might be right after they filmed Tabitha's final scene earlier this season.

A photo of Oswald looking shocked while some stuff blows up behind him. Maybe that's also at the warehouse, it's possible that Tabitha saves Barbara from Penguin and blows up the crashed helicopter with a rocket launcher.

There are some other photos of Bane, Lucius, Barbara, Riddler with his long hair, Ecco and Jeremiah dancing, GCPD cops, ...