Kati,
If you use PhotoBucket (or another off site hosting) then you need to copy the image URL (Photobucket makes that easy) and paste it here. I always just copy the "direct link". If you do that, you need to hit the "insert image" icon in the toolbar above the reply box (it looks like a picture of the moon over a mountain). Photobucket does offer a "BB CODE" option...if you select that, you should just have to paste the info into your reply.