Flash Player 9 is required to use idFindr... get it here

Use idFindr to find your Flickr userid, groupid and photosetid numbers.

You can find userid numbers by searching by email address, flickr username or by entering your flickr user page URL, all groups and photosets attached to that userid are listed, if any are found.

You can also get a groupid or photoset id directly by entering the group or photoset URL.

Some places where you can use your Flickr ids