Flickr uses the Frutiger font type. I used Fontslogo.com to help me identify this font. Some ways one can identify Flickr’s font is by first looking if it has any serifs. It doesn’t have serifs so that means its apart of the sans serif family. Then if you look closely at the “K” and how its upper leg is shorter than its stem you can identify it as Frutiger. Also the arch of the “F” is unique.