The key part of the process is that it has to be a third-party host. At the time, Photobucket was the biggie. Not so much anymore. As bodia said, you have Imgur, Flickr, and I believe there are a few others. I have my own hosting, so I use that. The process from the forum side, IMO, is really straightforward - you need a link to a picture. Where it gets complicated is how you get that link from the various sites (and they all seem a bit different). That, and the process can change - Google Images has changed their interface, and now you have to go through an extra hoop or two to get the link for a picture.