[Mr Guy]

Very short answer: No with a "but": You don't need one, but if you are intending to sell them to somewhere else, it will help to get one.

Slightly longer answer: Yes with an "if": In other words, it's for additional protection you technically shouldn't need, but unfortunately in our litigatious world it's much more cost effective to have that protective signature than it is to fight for your rights later, if you do intend to sell them or display them, and it will make it easier to sell them if you do have that signature to provide to anyone who does wish to publish them.

Long answer: No with a "but" and an "and":
The point tuxcomputers makes above is a sound one. Most of the advice here seems to be oriented around covering your butt the most fully in order to be able to sell pictures with the greatest of ease. It still all comes around to you, personally, not "needing" a release at all. No country I've yet been made aware needs any kind of permission to either take photographs or to sell them for commercial use, assuming you took the photo legally (Ie, trespassing laws, peeping tom laws). All the legal mumbo jumbo is about permission to USE the photograph in commercial means, meaning it's the publisher who is ultimately responsible. What you'll find here, however, is a lot of people who have apparently had run ins with either ignorant lawyers, shady lawyers, or lawyers using scare tactics to threaten them, or know people who have, and have come to the conclusion that being legally within their rights is not as important as avoiding potential legal hassle and expense to prove they were in the right later.