First off, let’s talk about conventions in general. They are large gatherings of like-minded individuals who share an interest in something. They often meet at hotels, or for larger events a convention center and the surrounding area. Most of my experience consists of Anime (Japanese animated videos, but often every aspect of Japanese pop culture) and Science-Fiction conventions as well. Given my level of experience with those two types, I will be talking about them for the most part when I give specific examples.
Conventions are a sub-culture of various forms of hobby from the aforementioned Anime, to art, video games, and even the creation of fish replicas. Convention photography centers around a relationship that forms at certain types of conventions. In Anime conventions for example, there are attendees who wear costumes of their favorite characters from videos, manga (comic books), or video games depending on what interests the individual most. It is a given that having hundreds or thousands of people in costume looking to be noticed will draw in photographers looking to take their photo.
Besides the dedicated photographers, photography at conventions is further broken down into subsets. First and foremost, there are a multitude of casual photographers who take snapshots of their favorite characters, their friends, and pretty much anything else they find of interest. As mentioned before, you have the serious photographers who roam the halls with extreme equipment and desire to take as many cosplayer photos as possible (cosplay meaning people who dress up in costume). You can also find booths where professional photographers offer their services for a price. It is actually quite a nice working relationship that develops between cosplayers and photographers. There is much fun to be had for both parties!
Various convention locations.