Stacy's post defining leeching is mostly correct, but not entirely. Leaching is hot-linking to someone else's site without their permission. This would occur if someone wanted to ask a question about one of Bruce Bump's knives, and attached an image of the knife, with the http:\ URL directly referencing the photo on Bruce's web site.
From that point on, every time someone opens the message thread from this forum and views that image, some bandwidth is used up at Bruce's internet host server. This "leeches" bandwidth from his server.
A more proper technique is to save the image to your computer, and then upload it to your own server. This "server" could be an online photo site, your website, a folder on your own server, etc.
Of course, you should be aware of copyright infringements, as well . . . but this has nothing to do with leeching.
Mike L.