Sometimes you may want to show an image attachment in the middle of some text, inside a topic description or a post, instead of at the bottom. To do this, type [image]filename.jpg[/image] where you want it, and where the filename of the attached file you want is filename.jpg. This will work as long as you've attached a file with that name to the same place (you can't reference a file from a different topic).
Don't confuse this with an [img] BB Code which would allow you to show an image from a remote URL.
As of WSN 10.0.18, the [image] tag now accepts a size parameter. Use this to generate a thumbnail of a specified size WIDTHxHEIGHT. For example, [image=300x250]filename.jpg[/image] will show a 300 pixel wide by 250 pixel tall thumbnail image of the filename.jpg attachment.