Silvercall- welcome to the forum. To insert an image from flickr, just copy the url of its location and then click on the "insert image" icon on the message composition window (it looks like a little picture of sun and hills).
The URL will then authomatically be bookended by [IMG] tags. Like this:
By the way, your image is clear proof that the Nokton 35 1.4 is a terrible lens for architecture...look at all those curved lines!