If you want to attach a large image to a discussion post, it is recommended that you re-size the image first. (Large images mean long download times which causes problems with dial-up users). Check out the following link to a free image sizing site.
http://www.shrinkpictures.com/
You may also want to check out http://flickr.com for uploading/editing/resizing pictures to share on blogs, wikis or facebook.
