on (the new) flickr you have to go to the 3 dots at the bottom right corner of the picture you're viewing, which brings up an option menu. click on "view all sizes"
choose the size you want, but DON'T copy the URL on your browser, you have to RIGHT CLICK on the "download this size" above the size listings, and choose COPY LINK ADDRESS (in Chrome, various browsers may say something similar).

if you did it right, the flickr link you end up pasting here will have "farm" and "staticflickr" in the link.

I also always choose to uncheck the box that says "retrieve remote file and host locally" when doing the image linking here on the boards.