# File lib/flickr/base.rb, line 391
        def url(size=nil)
                base = 'http://static.flickr.com'
                ext = (size == 'o') ? self.originalformat : 'jpg'
                return size ?
                        "#{base}/#@server/#{@id}_#{@secret}_#{size}.#{ext}" :
                        "#{base}/#@server/#{@id}_#{@secret}.jpg"
        end