Single images do not display in posts, whether using the full Flickr URL or the ID (as per "usage" on the plugin's wordpress.org page).
[flickr]http://www.flickr.com/photos/dancoulter/2619594365/[/flickr]- Inserts the given image. You can also just put the photo ID in there (the numeric string at the end of the link).
Even trying the example above doesn't work. There are a couple posts from the same person 9 months ago but it doesn't say how or if they resolved it.