
In poker, table image is how the opponents view you and your play. Everyone at the table has an impression of you, regardless of their skill. This is based on a number of things.
First of all, most good players watch how many hands you play and how you play them, to get an idea of how good you are, in an attempt to play better against you.
Secondly, if you are winning that day or not makes a difference. A player with rack after rack of chips in front of them will be treated differently because of this. In many players minds lucky and good are interchangeable.
Lastly, and least important, your appearance makes a difference. A person who is drinking and looking like they are having a good time will generally viewed differently than someone with sun glasses on and hat down, trying to look professional.
Table image is obviously more important when you play live, but many of the things carry over into online play too. The main point is that everyone at the table makes generalizations about you; this is how human knowledge works. Regardless of whether they are an expert trying to figure your play out, or a new player who doesn't make any extra effort, everyone sees you in a certain light.
Against bad players, you really shouldn't over think things. The best approach to beating them is to keep showing down the best hand. You wait for a good hand and make them pay -- get value. Experienced opponents are harder to do this to because they can see that you are waiting for good hands and can easily avoid the hands where you have a major edge. To beat very good opponents, you have to use some deception in your game. You use this to keep the opponents guessing so that when you do have a big hand, you get paid off.
One way of deceiving a thinking opponent is using your table image against them. Above I mentioned how humans "know" something: they generalize. There is so much going on in the world at once, that the only way to make sense of it is to see things as predictable and consistent and avoid variables that don't fit in. In poker, this basically boils down to players assuming you play one way, just because you have played that way in the past. This is a very important aspect of the game to understand and can take you from being an ABC solid player, to being someone who is more dynamic and dangerous. The vast majority of the time, players take a very rigid view of other players. After seeing them make a bad play, not play a hand for a while, or make a big bluff and get caught, they generalize -- and that's not bad thing. You should, like the other good players, watch opponent's play and base your decisions in future hands, in part, on how they played before. The problem with this though, is that for an expert player, it leaves open the door for manipulation. Let me make this a little more concrete with a few examples.
The first example of how this is important is its effect on your ability to get more than your fair share of the pots -- especially bluffing. I was in a big limit holdem game with good opponents. I knew they viewed me as a tight player, because I hadn't played many hands yet. I was dealt 88 under-the-gun. In this type of game, I consider that a "mixing up" kind of hand, and since I hand 't played a pot in a while, I came in for a raise. Everyone folded to an older Asian man who three bet me. He was a solid player so I assumed either he had a hand like AK or AQ or a bigger pocket pair. I called and the flop came back A-6-5. I checked and he bet. Now, since I didn't cap the betting preflop, as I would with KK, QQ or AA, there was a good chance that he assume I actually had the big ace. I decided that I would check raise him here and see what happened -- represent the Ace. I check raised, the thought a second and then mucked his hand.
The point of this example is that the reason this worked is because of my table image. He viewed my play in a certain way and since I knew how he viewed me, I could use that against him, to get more of an edge, without card power. It is very difficult for a good player to make a call like this since he knows I'm playing well. Now, if I got caught and he beat me, from that point forward my table image would be different. Now I wouldn't try that again, but I would be more aggressive with my good hands, because I expect players to call me down.
Another example: No limit game. Again, my table image is solid and tight. Players have only seen me show down solid hands. I come in for a raise with 76s, expecting to just take the blinds. I get reraised some, not a lot, by a solid player. I call. The flop is J-7-7. He bets and I check raise here. The reason I do that is because it shows that I most likely just have a Jack. He calls and goes all-in on the turn with KK, and I bust him.
Another example: If you are a tight player and occasionally raise with a weird hand, you usually win uncontested on the flop, if you have only one opponent. Why? Because the opponents assume that you have them beat, because you rarely raise.