code:

// ==UserScript==
// @name           EasyFlickrLink
// @namespace      what
// @description    Makes it easy to link back to Flickr when posting images in forums.
// @include        http://www.flickr.com/photos/*/*/*
// ==/UserScript==

if (document.getElementById("allsizes-photo") == undefined) {
var PhotoDiv = document.getElementById("photo-drag-proxy").nextSibling;
var PhotoElement = PhotoDiv.getElementsByTagName("img");
var PhotoURL = PhotoElement[0].src;
var MetaDiv = document.getElementById("meta");
LinkBoxDiv = document.createElement("div");
LinkBoxDiv.innerHTML =  "BBCode Link: <input type=\"text\" size=\"45\" value=\"[url=" + window.location + "][img]" + PhotoURL + "[/img][/url]\">";
MetaDiv.appendChild(LinkBoxDiv);

} else {

var PhotoDiv = document.getElementById("allsizes-photo");
var PhotoElement = PhotoDiv.getElementsByTagName("img");
var PhotoURL = PhotoElement[0].src;
var SizesURL = String(window.location);
var urlcutstart = SizesURL.indexOf("/sizes/");
var PhotoPageURL = SizesURL.substring(0, urlcutstart + 1);
LinkBoxDiv = document.createElement("div");
LinkBoxDiv.innerHTML = "BBCode Link: <input type=\"text\" size=\"45\" value=\"[url=" + PhotoPageURL + "][img]" + PhotoURL + "[/img][/url]\">";
PhotoDiv.appendChild(LinkBoxDiv);

}