Using photo bucket is the easiest way. That way all you have to do is copy and paste into your thread. You can get a photo bucket account for free.
Or, you can create an album in your User Control Panel and then click on the photo you want and copy the Image Tag and paste it in the text while making a post.
I use photobucket too! When you mouse over a pic you can copy the image code for simple click and paste anywhere in the reply box.