While working with a photographer—and setting up a proper photo shoot—is almost always preferable for a creative project, timing and budget constraints (or subject matter) often preclude their use. This is where stock photography, existing, searchable, commercial photography available online for license, comes in.

The stock photo world is a competitive one; acquisitions and mergers are common, and conditions are constantly changing. Here’s a brief introduction to the big stock photo providers and the types of stock photography available.

The major players
New stock photography companies seem to pop up daily, but there are a handful that endure.

Getty Images is the 800-pound gorilla of the stock photo world. Through their eponymous Getty Images site, their affiliated Shutterstock site, and their “budget” brand, iStock, Getty is unavoidable when it comes to searching for stock imagery. Each site is easy to use, so Getty, Shutterstock and iStock are natural “go-tos,” but there are plenty of other quality providers to check out as well, including Corbis, Veer, and Masterfile.

Before you start your search, though, familiarize yourself with the three general categories of stock photos available.

Rights-managed images
Rights-managed images are the way to go if you need something unique. Think national campaign and big budget. When purchasing a rights-managed image, the usage agreement will imply exclusivity. Because the image provider is offering you sole rights, the cost for rights-managed images tend to be much higher than for royalty-free images. Terms generally include language limiting you to a particular print run or amount of online impressions.

Royalty-free images
Not to be confused with pubic domain images, royalty-free images are those with a one-time fee, and allow usage across multiple instances and applications. To keep costs down, the usage agreement will include very specific language concerning image size, duration, and the type of industry the image will be used for. Think local or regional campaigns and smaller budgets. There are generally no limits to how often the image provider can sell the same image, though, so there’s always a risk that the same photo you use for your project may also show up elsewhere.

Images in the public domain
Public domain images are just that: images that for whatever reason—due to their age, origination, or, by express permission of the photographer—have ended up in the public domain. Use of images in the public domain are generally without restriction, though some government-sourced photos prohibit commercial use. Public domain images are a vastly underutilized resource, especially for historic images. Finding what you need can be difficult though, as no single source or web site for public domain photos exists. Often online databases are topic-specific, but, with a little searching, almost any imagery can be found.