I don't use the site but having a quick read it seems they've made it problematic on purpose,
"The direct link to a photo file is no longer shown on the page. Per the Flickr Community Guidelines "pages on other websites that display content hosted on flickr.com must provide a link from each photo or video back to its page on Flickr." Linking directly to the photo file doesn't do this."
We have an almost identical guide to what @hamtagger posted that they use on OS however it’s not really up to date and it looks like @raisinwing has a quicker way of doing it and I’d like to see a simplified guide.