I can't find any info on posting pics either and I'm not an expert but I'll try to help you out.
If posting a pic in a thread, you should either save it locally or your hard drive and attach it as a file or you can post the web link/url to the pic in your test if the pics are hosted on a website you use.
If posting a pic in the photo gallery, I have only had luck attaching pics that I have saved on the hard drive, not sure about linking to photos posted on a web site but hopefully someone else can help you there.
If you have photo editing software try to keep the pics from being huge but I believe the photo gallery can usually resize them. Hope that helps :bigups