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Document ID: 687 Branch: main Language: default Name: CaptchaReader Document Type: Document Created: 9/4/05 11:58:39 PM Creator (owner): Pier Fumagalli State: publish Parts ===== Content ------- Mime type: text/xml Size: 3366 bytes Content: <html> <body> <p>The <tt>CaptchaReader</tt> is a simple reader generating JPEG images for the text supplied as its source in a way so that it's hard to parse automatically. </p> <p><em>CAPTCHA</em> means quite literally <em>Completely Automated Public Turing Test to Tell Computers and Humans Apart</em> and one of the best resources on this can be found at the <a href="http://www.captcha.net/";>Carnegie Mellon School of Computer Science CAPTCHA project.</a>.</p> <p>This reader creates very simple <em>CAPTCHAs</em> from within a Cocoon pipeline, enabling quick and safe end-user presence identification. As an example, look at the following pipeline snippet:</p> <pre> <map:match pattern="*"> <map:read type="captcha" src="{1}"/> </map:match></pre> <p>The example will produce an image containing the text in "<tt>{1}</tt>" "warped" or "bent" in a way similar to the Adobe® Photoshop® "<em>Wave</em>" filter plugin.</p> <p>Few pipeline parameters control the operation of the <tt>CaptchaReader</tt> (this component is not configurable):</p> <ul> <li><tt>width</tt>: the width of the image to generate <em>(default: 100)</em>. </li> <li><tt>height</tt>: the height of the image to generate <em>(default: 50)</em>.</li> <li><tt>foreground</tt>: the text foreground color<em> (default: random)</em>. </li> <li><tt>background</tt>: the image background color <em>(default: white)</em>. </li> <li><tt>font</tt>: the font to use for the text <em>(default: serif)</em>.</li> <li><tt>scale</tt>: the scaling factor for interim images <em>(default: 5)</em>.</li> <li><tt>amount</tt>: the amount of text warping to apply <em>(default: 1)</em>. </li> <li><tt>quality</tt>: the JPEG encoding quality<em> (default: 0.75)</em>.</li> </ul> <p>Note that when the <tt>foreground</tt> parameter is not specified, the color used to write the text will be randomly chosen in a way that it contrasts well with the background color to avoid problems of illegible text.</p> <p>Both the <tt>foreground</tt> and <tt>background</tt> parameters accept strings in the format specified by <a href="http://java.sun.com/j2se/1.4.2/docs/api/java/awt/Color.html#decode%28java.lang.String%29";>Color.decode(String)</a> (for example <tt>fff</tt>, or <tt>0099CC</tt>) or one of the field names of the <a href="http://java.sun.com/j2se/1.4.2/docs/api/java/awt/Color.html";>Color</a> class (for example <a href="http://java.sun.com/j2se/1.4.2/docs/api/java/awt/Color.html#BLACK";>BLACK</a> or <a href="http://java.sun.com/j2se/1.4.2/docs/api/java/awt/Color.html#cyan";>cyan</a> ...).</p> <p>The <tt>scale</tt> parameter controls how much the specified size should be scaled while processing the interim images: the bigger the scaling factor, the better the image quality, but also the memory used while generating the final image will be bigger. In other words, use this with care.</p> <p>The <tt>amount</tt> parameter is interpreted as a floating point number and must be greater than zero. This controls how much text should be warped, and normally a value of 1 produce quite-good warping. Increasing (or decreasing) this value will produce more (ore less) warping.</p> <p>Remember that in no way the <tt>CaptchaReader</tt> claims to be able to generate "unbreakable" text (that will be impossible), and improvements to the algorithm are welcome.</p> </body> </html> Collections =========== The document belongs to the following collections: documentation
