You can place a photo in a post by using the image UBB code and pointing the URL to a "hosted" pic.
For example, when you reply to a posting like I am right now, underneath the post box where you type, in the middle column it says "Instant UBB Code". As I'm typing, if I click on the word "Image" in the ubb code box, then I get a dialog box asking for a URL. When I fill in the URL I get this:
This is a picture from my website. You can tell by right clicking on the picture and looking at the properties. If you want to post a picture that you have, then you need to have it hosted somewhere. Most ISPs these daya give you free web space with your Internet account. If you don't have your own web site, there are a few that will host stuff for free (search google for "free web hosting" or "free image hosting").