A little clarification:

If you use this website, you'll be asked for the "Photo_ID" and the "secret" (i.e., a hashed code). The numerical portion of the URL is the ID and the secret is the alphanumeric string. I think, though I haven't tested this extensively, that you only need the "ID" for public photos. If the photo you're looking for is private, then you'll also need to supply the "secret" code. (And if it is private, and you aren't logged in with an account with viewing rights, then finding the Flickr page for the photo will take you to a "You don't have permission" error.) For public photos, supplying the ID only ought to work.

For the example given above, viz.:
http://farm3....

A little clarification:

If you use this website, you'll be asked for the "Photo_ID" and the "secret" (i.e., a hashed code). The numerical portion of the URL is the ID and the secret is the alphanumeric string. I think, though I haven't tested this extensively, that you only need the "ID" for public photos. If the photo you're looking for is private, then you'll also need to supply the "secret" code. (And if it is private, and you aren't logged in with an account with viewing rights, then finding the Flickr page for the photo will take you to a "You don't have permission" error.) For public photos, supplying the ID only ought to work.

For the example given above, viz.:
http://farm3.static.flickr.com/2411/2237119567_e1e640b249.jpg

The ID is 2237119567
and
the "secret" code is e1e640b249

Here's what you get with the Google search method...