I'm only going to talk about the basics - most of these are common-sense or basic manners. A few of them are things that photo subjects should know, too.
And no, I'm not an expert. I'm a hobbyist who takes his hobbies seriously (as anyone who has read this blog at any length should already know). I'm not a professional photographer, nor am I an attorney. Much like my strategy articles, it will not be hard to find people who disagree with my statements.
As a photography subject, you need to know that you've already given GenCon permission to take your picture (and use your likeness in their advertising). It's in their Terms & Conditions:
In other words, just by attending, you have given the convention (and its licensees) the right to take your photo and to use that photo in their advertising. What I don't know is if other attendees or exhibitors are considered licensees or not. It's theoretically possible, however. Either way, you have given up a portion of your Right to Publicity.EXPLOITATION OF NAME AND LIKENESSIn consideration of being allowed to participate in this Convention, I hereby agree that GEN CON may photograph and/or record my likeness and/or voice and my participation in the Convention and without any additional consideration, I hereby agree that GEN CON and its assigns and/or licensees may distribute, exhibit, broadcast, exploit, advertise, publicize and promote my name, biographical material, likeness, voice and performance in and in connection with the Convention or other GEN CON events. I further agree that GEN CON may edit my appearance therein and I waive any personal or proprietary rights with respect thereto. I represent and warrant to GEN CON that I have not made any contract or commitment in conflict with this grant of rights to GEN CON. Nothing herein contained shall obligate GEN CON to make or cause to be made any broadcast or other use of said appearance, or to exercise any of the rights granted to GEN CON herein.
Most conventions have this paragraph (or something very similar) in their T&C.
Even if attendees aren't considered licensees, you should also be familiar with a term called a "reasonable expectation of privacy." As far as Photography is concerned, in simple English, it boils down to, "If you're in public, you might be photographed." It's legal for photographers to take pictures of people who have no reasonable expectation of privacy. In a crowded convention hall, you have no reasonable expectation of privacy. There are exceptions here and there - for example, many grocery stores have "no photography" signs posted at the entrances. In those places, you should be safe from cameras - but a good rule of thumb is that you can be photographed while in public.
It should go without saying, by the way, that restrooms and changing rooms are places where you do have a reasonable expectation of privacy, and photography there without your consent is illegal.
Now, as a photographer, here are a few things to keep in mind:
Yes, really. If the person whose photo you want to take is already posing for one or more photos, go ahead. But otherwise, be polite. The words you want to use are, "Excuse me, may I take your picture?" Or some variant thereof. Just because you can legally take a picture doesn't mean you should.
Try To Get Out Of Traffic
GenCon has terrible traffic, and it's far from the only convention in this state. Getting from one point to another is difficult. As a vendor, I often had a number of boxes in my hands as I tried to navigate. A clump of people crowding a cosplayer who is posing for photos can lead to even worse traffic.
Some of this is unavoidable - there are areas where photography just can't be done without snarling traffic. In these cases, try to take the photo and move on.
This is something that goes for subjects as well as photographers, too. When you just stop, you create backups.
Try to get over to the side, where there is less traffic. This allows for better photos, too, because it reduces the distracting background problem that you see in so many cosplay photographs.
Don't be That Guy
I can't even count the number of times I saw cameras (and phones) which were aimed at chests instead of faces at the show. Believe it or not, it is noticeable. From both sides of the camera. And it's really not cool.
Yes, women have breasts. Don't make them your focal point. If you have manual control over your focus, make sure that her eyes are the focal point of your photo. If you're using a point-and-shoot or a phone, many of those have facial recognition these days, too. And you should be able to get the face and the rest of her costume into the same photo. Unless you're doing something unusual - and, if you are, talk to the subject first. "I want to get a shot of the embroidery detail on your sleeve," or "Can I get a better shot of your tattoo?" - this goes double and triple when your detail is on someone's chest or rear end (whether the subject is male or female).
Respect the "No."
If you ask to take a photo and your prospective subject turns you down, respect that. Don't hound them or whine. They may be on their way to an event, or just tired of being photographed so much. Let it go. Yes, you do have a legal right to take the picture (because they are in public), but that doesn't mean you should take that photo. It's one of those places where legal and right don't have the same meaning.
Don't Use Flashes At A Tournament or Other Event
Many people take their tournaments very seriously. A flash can distract someone for that critical second, costing them the game. If this means you need a tripod or other stabilizer to take the picture, then do it. If it's a tabletop RPG session of some sort, the flash can throw the GM off and make the game less-fun for all.
Really, you should try to be as invisible as possible at these.
If you're using an SLR, you should have some aperture control. Just throw your camera into Aperture Priority mode and open that aperture as wide as you can. Even indoors, you should be able to get decent-enough shutter speed that you won't need a tripod. If you can't, then you brought the wrong lenses - I get decent shots at f2.8. It means you need to play attention to your depth of field, as it'll be pretty shallow - but you should still be able to get good shots.
When Photographing a Tournament, Share the Love
If you're taking a picture of your son/daughter/boyfriend/girlfriend, that's one thing. But if you're photographing strangers playing in a tournament, don't focus on one person. Because that's really creepy and - if they notice - can make them uncomfortable which can effect the outcome of the tournament. Remember: When photographing tournaments and other scheduled events, you want to be completely invisible.
Don't Forget Unusual Angles
My wife hates having her picture taken. A lot. But she trusts me to take her picture, because over the years, I've shown her that you can take good pictures without highlighting what she thinks of as undesirable traits (my argument - that she has no undesirable traits - doesn't seem to hold much water with her). The photo to the right, for example, is one of her favorite photos that I've taken of her. Personally, I find it a little blurry and not all that spectacular, but she really loves it. Enough that she has used it as her userpic on several sites. It also highlights the Rule of Thirds pretty well - the arm of her glasses draws the eye immediately. Were I re-shooting (or cropping) this one, I'd shift the camera up or down a bit and to the right so that her eye is in that sweet spot, instead of the arm of her glasses.
At a convention, you won't always have enough time to earn any sort of degree of trust - in fact, you very rarely will. But keep in mind that some of the best (and most striking) portraits don't show the full face/body/whatever. But - if you're shooting an unusual angle, try to make your subject aware of your presence and your goal. Otherwise, you run the risk of looking - again - like a creeper.
People also look thinner when they are looking up at the camera. And - realistically - many people want to look thinner (myself included). If you're short and can do so, hold your camera up. Just be careful to avoid looking like you're just trying to get a down-the-shirt cleavage shot. Because that is tremendously creepy.
Be Prepared to Show the Photo to the Subject
One of the advantages of shooting digital is the ability to show the subject the photo immediately. If they ask to see your photo, show it to them. Seriously. Don't waffle, don't mumble. Even if it's a terrible photo, let them see it. They were kind enough to smile or pose for you - it's the least you could do. If it's a bad shot, offer to delete and re-take it. If they think it's a bad shot, make the same offer. Yes, really.
You should also be willing to provide them with a link where they can see it later. I put most of my pics up on Flickr. Knowing that in advance allows me to print up business cards with the URL where the photos will appear "in a few weeks." This also gives you time to tweak the image if you don't got directly from camera to website (or if, like me, you sometimes shoot film).
I could probably go on about this for a while - and throw in more technical detail - but, realistically, if you haven't caught what I've said so far, then anything else will be too much.
And, if I have lost you earlier, here is the main point you need to remember as someone with a camera at a convention: Treat your subject with respect. If you follow that one rule, I think you'll find that your photos will be the better for it.