The image brackets are only for links to images from the net. To upload pictures of your own, go to the "additional options" link below your post, and click the "choose file" button to attach an image from your computer.
This will only put a thumbnail of the picture below your post. you will need to get click on the image and copy the link, then go back to your post to insert it inside a post using the image brackets.
Also, there is a thread designated for uploading images. It is stickied under the project announcements board. You can upload your pictures there, then go back to your own thread and link the images in your post.
Hope that makes sense!
