In Flickr, if you click on the Share icon (the arrow in the rectangle), you'll find an option "Grab the BB/HTML code".

Change the option to BB code and it will give you all you need to copy and paste straight into a post here.

It will look like this

HTML Code:
[url=http://www.flickr.com/photos/numbers/][img]http://farm8.staticflickr.com/numbers[/img][/url]
[url=http://www.flickr.com/photos/numbers/]Untitled[/url] by [url=http://www.flickr.com/people/numbers/]paulbot[/url], on Flickr