The web is exploding with images, and an awful lot of them are getting there through social media. Thanks to a relatively new generation of online services, billions of user-generated photos are now live on the web. About two dozen websites specialize in image hosting and/or photo sharing, and more are showing up every day. Most of these services are fairly accessible, but the range of tools and technologies can be confusing. Here's what you need to know to pick the photo-sharing service that's right for you.