DJANGO | TESSERACT | INKSCAPE | GIMP | PYTHON | QCCPACK LINUX JOURNAL ™ TESSERACT OCR PIXEL CREATOR SPEAKS INKSCAPE SCALABLE IMAGE PROCESSING VECTOR GRAPHICS DEEP GIMP ALTERNATIVES REAL-WORLD Since 1994: The Original Magazine of the Linux Community SELINUX JULY 2007 | ISSUE 159 AUTOMATED GIMP Django | Tesseract | Inkscape | GIMP | Python | SHREK QccPack | THE THIRD Blogging Linux Feeds an Ogre | Pixel | SELinux JULY www.linuxjournal.com USA $5.00 | CAN $6.50 2007 ISSUE QccPack Python Command-Line Driven 159 U|xaHBEIGy03102ozXv+:= + Image Processing Image Gallery Manage Any Data Center. Anytime. Anywhere. Avocent builds hardware and software to access, manage and control any IT asset in your data center, online or offl ine, keeping it, and your business, “always on”. Visit us on our Remote Control Tour. For locations near you, go to Avocent, the Avocent logo and The Power of Being There, are registered www.avocent.com/remotecontrol. trademarks of Avocent Corporation. ©2007 Avocent Corporation. AvocentRemote_LinuxJournal.indd 1 5/8/07 1:01:52 PM JULY 2007 CONTENTS Issue 159 FEATURES 38 DREAMWORKS ANIMATION SHREK THE 54 INTERVIEW WITH PAVEL THIRD: LINUX FEEDS AN OGRE KANZELSBERGER, CREATOR OF PIXEL What can you do with Linux and 20 million CPU render hours? Photoshop comes to Linux, sort of. Robin Rowe James Gray 44 TESSERACT: AN OPEN-SOURCE OPTICAL ON THE COVER CHARACTER RECOGNITION ENGINE • Tesseract OCR, p. 44 If you really need OCR. • Pixel Creator Speaks, p. 54 • Inkscape Scalable Vector Graphics, p. 48 Anthony Kay • Deep GIMP Alternatives, p. 34 • Real-World SELinux, p. 84 48 INTRODUCING VECTOR GRAPHICS • Automated GIMP, p. 58 • Shrek the Third: Linux Feeds an Ogre, p. 38 AND INKSCAPE • QccPack Python Image Processing, p. 80 Want scalable beauty? • Command-Line Driven Image Gallery, p. 70 Marco Fioretti COVER PHOTO COURTESY OF DREAMWORKS ANIMATION LLC. 2 | july 2007 www.linuxjournal.com Keep it simple. Rest easy. High technology is exciting. But all too often that includes pointless complexity. Not with Coyote Point. From local to global load balancing, application acceleration or ultimate network manageability, Coyote Point leads the pack. We take the guesswork out of application traffic management to deliver reliable solutions. You won’t find anything faster, smarter or more affordable out there. Find out why more than 2,000 businesses save time, money and mental energy with Coyote Point. Write [email protected] or call 1-877-367-2696. A coyote is a creature of elegant simplicity. Your network should be, too. Copyright © 2007 All Rights Reserved. www.coyotepoint.com JULY 2007 CONTENTS Issue 159 COLUMNS INDEPTH 18 REUVEN M. LERNER’S 58 AUTOMATED GIMP AT THE FORGE PROCESSING OF WEB IMAGES First Steps with Django Program GIMP to work for you. Ben Martin 22 MARCEL GAGNÉ’S COOKING WITH LINUX Let Me Show You How It’s Done with a Little Video 54 PIXEL CREATOR PAVEL KANZELSBERGER 26 DAVE TAYLOR’S WORK THE SHELL Displaying Image Directories in WRITING YOUR OWN IMAGE Next Month Apache, Part IV 70 GALLERY APPLICATION WITH 28 DOC SEARLS’ THE UNIX SHELL LINUX FOR SUITS GUI? We don’t need no stinking GUI. COOL PROJECTS Beyond Blogging’s Black Holes Girish Venkatachalam You can buy an old coin-slot arcade machine and play some- 96 NICHOLAS PETRELEY’S 74 PROGRAMMING PYTHON, thing like Pac-Man on it, but how /VAR/OPINION PART II about if you could convert it to a Amazing Free Distributions Abound More love for learning Python. Linux-based arcade machine that José P. E. "Pupeno" Fernàndez lets you play all of your favorite QUICK TAKES 80s arcade games and more? If 80 IMAGE PROCESSING WITH that isn’t a cool project, we don’t 34 DEEP IMAGES QCCPACK AND PYTHON know what is. We’ll show you how to modify the case, hook up Dan Sawyer A library collection for Python joysticks and buttons—the works. image processing. Want to create your own virtual Suhas Desai private network for your Nokia E61? We’ve got that, too. 84 MAMBO EXPLOIT BLOCKED BY SELINUX As always, there’s much more. SELinux catches exploits. What if building your own Richard Bullington-McGuire Firefox add-on/extension is your definition of cool? We’ll walk you through the whole process. ROLE-BASED SINGLE SIGN- 90 We also take a peek at some of ON WITH PERL AND RUBY the freshest cool projects others IN EVERY ISSUE Let the role dictate the privileges. have created. Robb Shecter 8 LETTERS 12 UPFRONT 16 TECH TIPS USPS LINUX JOURNAL (ISSN 1075-3583) is published monthly by Belltown Media, Inc., 2211 Norfolk, Ste 514, Houston, TX 77098 USA. Periodicals postage paid at Houston, Texas and at additional mailing offices. Cover price is $5 US. Sub scrip tion rate is 32 NEW PRODUCTS $25/year in the United States, $32 in Canada and Mexico, $62 elsewhere. POSTMASTER: Please send address changes to Linux 81 ADVERTISERS INDEX Journal, PO Box 980985, Houston, TX 77098. Subscriptions start with the next issue. 4 | july 2007 www.linuxjournal.com Editor in Chief Nick Petreley, [email protected] Executive Editor Jill Franklin [email protected] Senior Editor Doc Searls [email protected] Art Director Garrick Antikajian [email protected] Products Editor James Gray [email protected] Editor Emeritus Don Marti [email protected] Technical Editor Michael Baxter [email protected] Senior Columnist Reuven Lerner [email protected] Chef Français Marcel Gagné [email protected] Security Editor Mick Bauer [email protected] Contributing Editors David A. Bandel • Greg Kroah-Hartman • Ibrahim Haddad • Robert Love • Zack Brown • Dave Phillips • Marco Fioretti • Ludovic Marcotte • Paul Barry • Paul McKenney • Dave Taylor Proofreader Geri Gale Publisher Carlie Fairchild [email protected] General Manager Rebecca Cassity [email protected] Director of Sales Laura Whiteman [email protected] Regional Sales Manager Joseph Krack [email protected] Regional Sales Manager Kathleen Boyle [email protected] Circulation Director Mark Irgang [email protected] Marketing Coordinator Lana Newlander [email protected] System Administrator Mitch Frazier [email protected] Webmaster Keith Daniels [email protected] Accountant Candy Beauchamp [email protected] Linux Journal is published by, and is a registered trade name of, Belltown Media, Inc. PO Box 980985, Houston, TX 77098 USA Editorial Advisory Board Daniel Frye, Director, IBM Linux Technology Center Jon “maddog” Hall, President, Linux International Lawrence Lessig, Professor of Law, Stanford University Ransom Love, Director of Strategic Relationships, Family and Church History Department, Church of Jesus Christ of Latter-day Saints Sam Ockman, CEO, Penguin Computing Bruce Perens Bdale Garbee, Linux CTO, HP Danese Cooper, Open Source Diva, Intel Corporation Advertising E-MAIL: [email protected] URL: www.linuxjournal.com/advertising PHONE: +1 713-344-1956 ext. 2 Subscriptions E-MAIL: [email protected] URL: www.linuxjournal.com/subscribe PHONE: +1 713-589-3503 FAX: +1 713-589-2677 TOLL-FREE: 1-888-66-LINUX MAIL: PO Box 980985, Houston, TX 77098 USA Please allow 4–6 weeks for processing address changes and orders PRINTED IN USA LINUX is a registered trademark of Linus Torvalds. TotalView® Introduces The Most Powerful Command For The Multi-core Age. TotalView is the proven debugging solution built specifically to address your unique challenges when developing multi-core, multi-threaded applications. As part of a complete suite of proven multi-core debugging and performance tools that supports C, C++ and Fortran on Linux, UNIX and Mac OS X, TotalView 8.1 is the only solution you can count on for all of your multi-core debugging needs. Developed to help debug the world's most demanding applications, TotalView is extremely powerful, yet easy to use. Visually-driven, it provides enhanced graphical representations that enable users to quickly recognize problems and zoom in to identify root causes. TotalView does not require instrumentation, relinking, or rebuilding. TotalView has been proven to reduce debugging time by up to 80%. Try it now, for free! Go to www.totalviewtech.com/command to power-up your 15-day trial version, or call 1-800-856-3766 for more information. Built for the Multi-core age © 2007 TotalView Technologies, LLC TotalView is a registered trademark of TotalView Technologies, LLC. All other names are trademarks of their respective holders. letters love Ajax. I use it in my JSPs all the time. But non-Web development topics that can be come on! It’s not a Linux technology, but yet covered in At the Forge? it gets coverage in almost every issue of LJ -- since at least October 2006. Marc Let’s take a look back: We’ll do our best to cover different ground. However, Ajax is an extremely popular • October 2006: At the Forge—“JavaScript, approach to providing users with a rich-client Forms and Ajax”. experience. Its platform-neutrality and the • November 2006: At the Forge— broad set of Linux tools available make it an “Beginning Ajax”; Feature—“Caller ID excellent Linux topic.—Ed. with Asterisk and Ajax”. • December 2006: At the Forge—“Ajax Ajax Appreciated Application Design”. I just wanted to tell you your coverage of Ajax, • January 2007: At the Forge—“Prototype” Ruby and programming languages, hot topics (Ajax); Indepth—“Ajax Timelines and the in the industry, is just awesome. I am glad I Semantic Web”. bought a subscription from you guys. I am a • February 2007: At the Forge— Linux hobbist/Web developer/graduating senior “Scriptaculous” (Ajax). from ASU Polytechnic and just wanted to let • March 2007: A nice break from Ajax. you know you are doing an awesome job. Ajax Overdose • April 2007: At the Forge—“Dojo Events -- First let me say that I love your magazine. and Ajax”. Karol I look forward to each issue and I enjoy • May 2007: Ajax everywhere! almost every article...yes, even you Marcel.