At the top of your screen, there is a blue bar with options you can click on; Index, User list, Rules, Search, My Page, etc. etc. in there is Upload. Click it, hit browse, find your desired pic on your computer, hit Upload, your pic will appear and the URL and image code will be under it, copy and paste that back here into a post.
go to the top of the byc page you are on and click uploads. browse for your pic then upload and copy the adress it gives you and paste that into your post. im pretty sure that will work
once you have all the photos uploaded, click that upload screen closed.
then re-click on the upload option at the top of you're page and the upload page will open with all your photos.
It is there that you copy and paste from the "image" or "thumbnail" bar under each individual photo.
Since the upload screen is it's own screen, you can go to "post a reply" and type your message and then copy/paste your photos by flipping back and forth between the two.