Okay this is going to be long, maybe a little rambling, and full of SPOILERS.

The interpretation of the ending is going to depend a lot on your interpretation of the film.

For me, the film is primarily about the cycle of violence and how people can be trapped in a cycle that spans generations.

We start off with the story of a previous winter caretaker, Grady, killing his two little girls 'about 8 and 10' his wife, and stacking them neatly in a room and killing himself.

Danny encounters two girls while riding his big wheel but they are twins and are shown strewn across the hallway one facing up one facing down.

Later in the film we meet a Grady in the gold ballroom/red bathroom. This Grady is a waiter, not the winter caretaker. He tells a story about 'correcting' his wife and daughters when they attempted to leave the overlook.

Additionally, early on in the film Wendy tells a story of Jack dislocating Danny's arm after drinking with Wendy concluding it by saying ' ... he hasn't had any alcohol in, uh, five months."

Later in the film Jack tells a similar story to Llyod, the ghost bartender. However, Jack says his story happened 5 years ago.

Kubrick sets up a pattern of repeated stories similar to ones we have heard earlier in the film but with certain details off implying that these stories may not be the same. Instead they may be other instances of violence that establish a cycle of abuse across generations.

Also scattered through out the film are references to violent conflict with Native American's, not only the stories of the actual attacks but visuals like Jack throwing a ball against Native American figures in the lounge similar to an axe swing.

There are many suggestions of Danny being sexually abused by Jack. Danny laying on the bear pillow with his pants removed and hands over his genitals. This imagery is reinforced by the man in the bear outfit performing oral sex on another man at the films climax. There is also Jack and Danny's conversation in the apartment suite with Danny on Jack's lap.

These messages of domestic and sexual violence are reinforced subtle visual through the use of appearing and disappearing props and costumes.

When Danny talks to Tony we see a shot of Danny in the bathroom looking in a mirror (another major motif in the film of truth/reality being revealed in mirrors). The camera pushes in past the door to Danny's bedroom. There is a sticker of Dopey, one of the seven dwarfs, on Danny's bedroom door. Later, after Tony show's Danny something in the mirror, the sticker of Dopey is gone implying Danny has learned something important and is now slightly less innocent.

You can also notice that the bear rug in the Colorado Lounge only appears when Jack is also in the room, linking Jack to the bear/sexual abuse symbolism.

When Wendy first appears in the apartment she is dressed almost identically to a figure of Goofy hanging on Danny's wall. Wendy's 'goody' costume implies her denial of Jack's alcoholism, violent tendencies, and possible sexual abuse of Danny.

You will also notice that, generally, characters that are naive, in denial, or childlike tend be to dressed in a red, white, and blue color palette where as more mature, reality based, adult characters tend to be in earth tones. Jack starts off in earth tones and ends up in red and blue flannel and jeans. Wendy starts in red and blue and end up in earthtones. Danny, being a child, stays mostly in reds and blues but the become more muted or adult throughout the film as he confronts what is happening.

And of course there is the on going images of mazes through out the film starting with the yellow VW Bug winding up the mountain road, the hedge maze itself, the maze like interior of the hotel, the maze like carpet on the second floor that appears to trap Danny while playing with his toys, and the long twisting and turning tracking shots of characters running through the hedge maze as well as the hotel.

So what does all of this have to do with the ending?

Jack's body is trapped, frozen in the hedge maze. Jack's mind is trapped in the maze like Overlook hotel.

Where as Wendy and Danny were able to escape the cycle/maze of violence.

If you accept that the film is primarily examining violence (domestic and against racial/demographic groups), the cycle of violence (the repeated, but slightly altered, stories of child abuse and murder), and the difficulty of escaping this cycle (the maze like interior and exterior of the hotel) then the ending is simply a confirmation that, like Grady, Jack has '... always been here.'

Why is Jack's mind/soul represented by a photo on the wall? Because it is possible that nothing we have watched, especially anything that happens in the hotel, and especially especially anything that happens on the second floor is happening in the real world at all but that we are watching the memories/hallucinations/flashbacks of the main characters. That the hotel is actually the interior of one, or all, of the characters minds.

Evidence that the hotel isn't real:

The layout of the hotel is impossible

- The windows in Ullman's office shouldn't exist. There is a hallway and the 'blood' elevator bank directly behind Ullman's office.
- Background characters enter from unseen doors at the end of tour of the Colorado Lounge
- Halloran, Wendy, and Jack enter the freeze from a door on the right side of the hall but exit from a door across the hall along the left hand side.
- We never see how the Gold room or the apartment connect to the lobby/Colorado Lounge.
- The apartment has a line of windows in the living room and bedroom that should not exist. Based on exterior shots and when Wendy drops Danny out of the bathroom window the other windows should all be along an interior, windowless wall.
- The Red bathroom seems like it should be occupying the same space as the Gold ballroom.
- The entrance to the Maze is never the same twice.

Objects do impossible things

- The bear rug in the Colorado lounge appears and disappears, as does the drift wood sculpture.
other chairs and props appear/disappear sometimes within the same scene. Jack's typewriter changes models when he argues with Wendy in the Colorado Lounge. The chair behind Jack appears and disappears in the same scene. This implies that the argument with Wendy might not even be real but simply a hallucenation of what Jack wish's he had said to Wendy but only imagined it.
- The TV in the Colorado Lounge is not plugged in.
- All the furniture under the pictures shown at the end of the film has moved out of the way.

The second floor might not be real

- Wendy never is never actually seen on the second floor (she comes close when attacking Jack with the baseball bat but never makes it)
- There are numerous 'impossible' doors on the second floor.
- When Danny goes to get his fire truck we see him a few scenes later on the second floor with all the toys he had while playing in front of the TV in the Colorado lounge but the firetruck is missing. This implies the scene is actually a flashback/memory of possible sexual abuse of Danny by Jack when Danny goes for the firetruck, sits on Jack's lap, and the returns to the Colorado Lounge with his clothing torn.
- Jack has disturbing vision in the bathroom of beautiful woman revealed to be a rotting body when viewed in the mirror, similar to Danny's vision of something in the bathroom mirror at the beginning of the film.
- When Jack leaves room 327 the hallway lights are out, Jack backs away in darkness, implying he denies the vision in the bathroom, a vision of sexual desire revealed to be something horrific and repulsive (such as molestation)

When ever Danny rides his big wheel there is always exit on the right

- When Danny sees the Twins in the hallway there is an exit on the right side of the hallway
- When Danny first confronts room 237 there is an exit on the right side of the hallway
- When Danny escapes Jack in the maze in the finale he jump through the opening on the right.
Is this foreshadowing or a memory/plan of escape?

Other weird stuff

- Jack is reading a PlayGirl magazine in the hotel lobby
- Whenever Danny stops in the kitchen there are always a set of knives over his head
- What's with all the signs/reminders, almost like thought bubbles, every where?
- A car is scene driving directly at the entire family as they cross from the maze back to the hotel on the initial tour. The car never stops instead we just cut away second before the family would have been struck.
- Jack's 'stare' implies him drifting off into thought/fantasy turning large portions of the film into possible fantasies/hallucinations. We actively see this in the Gold room bar Lloyd scene were he 'stares' just before seeing Lloyd and seems to shake himself from though when Wendy enters screaming. Also, jack 'stares' again when Wendy visits to see how the work is going. Wendy walks up, Jack stares, the typewriter changes, a chair disappears, and the research book next to him flips to another page. After Jack blows up at Wendy the typewriter, chair, and book all return and Wendy acts as if nothing happened implying it all happened in Jack's mind.
- Jack slams the tennis ball on the floor of the lobby near a Mickey Mouse doll laying face down in a similar spot/position as Hallorann after he is killed.
- Jack slams a tennis ball against the Indian figures in the Colorado Lounge similar to his axe swing at the bathroom door.
- The only character we ever actually see working to take care of the hotel is Wendy.

Overall the film is insanely dense, re-watchable, and open to an amazing amount of interpretation depending on what you see as important, symbolic, and real.

What does the ending mean? Ultimately, the genius of The Shining is that the ending can mean almost anything you want it to mean.