For "advanced users" there are more options using [attachment=n][/attachment] bbcode (where n is the number of the attachment in the post,)
o attachment => Show full expanded picture
o attach => Show thumbnail, expandable to full picture
o attachthumb => Show thumbnail ONLY, not expandable
o attachmini => Show thumbnail, expandable to full picture
o attachurl => Shows attachment size, iamge dimensions, and download count; no picture