Phony Photo
Luke sends a photo of him with two women to the prisoners after he escapes. It's a symbol of hope for the men as it lifts their spirits about one day being free. Unfortunately for the men Luke admits the photo is a phony. That he paid a week's worth of wages to have it made.
Sunglasses
Boss Godfrey never talks. He holds his cane over his head as a symbol for a man to bring him his rifle. He is a crack shot with it, and never misses. Dragline calls Godfrey the man with no eyes because he always wears sunglasses and every time we see his sunglasses we see the prey he is about to kill. His sunglasses become a symbol of his violence and when he has something/someone in his sights he doesn't miss.
Into the Sun
Luke is fighting Dragline and getting his head beat in by him. So much so that he's eventually knocked down with every punch the much larger man throws. While on the ground, Luke looks up to see Dragline standing in the sun which blocks his view of his opponent. The image symbolizes Dragline's power, that he is superior and cannot be defeated by Luke, and yet he continues anyway.
Digging His Own Grave
After being caught and returned to prison for the third time he's made to dig a trench hour after hour, digging it out and refilling it. Late in the night we see Luke standing in the grave before being hit over the head by one of the bosses. He falls into the ditch and it looks like he has dug his own grave. It's a symbol that Luke has been broken. His ability to be free is over as the boss has killed his spirit.
Doorways
In the film, the director uses doorways in a very specific way in order that they take on a greater meaning. A doorway isn't an exit to any free place. Instead, it is an entrance from one prison to the next. No matter what door Luke goes through, he is not free.
