From owner-freebsd-questions@FreeBSD.ORG Sun Sep 6 17:34:25 2009 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 5BE1410656C2 for ; Sun, 6 Sep 2009 17:34:25 +0000 (UTC) (envelope-from freebsd-questions-local@be-well.ilk.org) Received: from mail6.sea5.speakeasy.net (mail6.sea5.speakeasy.net [69.17.117.8]) by mx1.freebsd.org (Postfix) with ESMTP id 3374F8FC22 for ; Sun, 6 Sep 2009 17:34:25 +0000 (UTC) Received: (qmail 8883 invoked from network); 6 Sep 2009 17:34:24 -0000 Received: from dsl092-078-145.bos1.dsl.speakeasy.net (HELO be-well.ilk.org) ([66.92.78.145]) (envelope-sender ) by mail6.sea5.speakeasy.net (qmail-ldap-1.03) with SMTP for ; 6 Sep 2009 17:34:24 -0000 Received: from lowell-desk.lan (lowell-desk.lan [172.30.250.6]) by be-well.ilk.org (Postfix) with ESMTP id 1A67F50837 for ; Sun, 6 Sep 2009 13:34:18 -0400 (EDT) Received: by lowell-desk.lan (Postfix, from userid 1147) id 984B91CC5D; Sun, 6 Sep 2009 13:34:17 -0400 (EDT) To: freebsd-questions@freebsd.org References: <64c038660909050933h25a91edcw56688993f5557ad2@mail.gmail.com> From: Lowell Gilbert Date: Sun, 06 Sep 2009 13:34:17 -0400 In-Reply-To: <64c038660909050933h25a91edcw56688993f5557ad2@mail.gmail.com> (modulok@gmail.com's message of "Sat\, 5 Sep 2009 10\:33\:03 -0600") Message-ID: <44skf0c6zq.fsf@lowell-desk.lan> User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.3 (berkeley-unix) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Subject: Re: Is there such thing as a 'soft checksum' tool? X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 06 Sep 2009 17:34:25 -0000 Modulok writes: > I'm not even sure such a tool exists, but it's worth asking: > > I'm looking for a pseudo-checksum tool for use with catalogging > images. For example, a strict checksum algorithm, like the sha family, > will produce a dramatically different checksum for two files which > differ by only a single bit. I'm looking for something where two > images images, which are similar, get a proportionally similar > checksum. When I speak of similarities I'm referring to their image > patterns. i.e two images of differing sizes, which are otherwise > identical, would produce very similar checksums. So the closer the > checksums are, the more similar two given images are. > > Does anyone know of anything like this? It turns out this is a remarkably hard problem. You can look at p5-Image-Compare, but be prepared to experiment before trusting the results. -- Lowell Gilbert, embedded/networking software engineer, Boston area http://be-well.ilk.org/~lowell/