| The
CaptchaReader is a simple tool generating JPEG images for the text
supplied as its source in a way so that it's hard to parse automatically.
CAPTCHA means quite literally Completely Automated Public Turing
Test to Tell Computers and Humans Apart and one of the best resources on
this can be found at the Carnegie Mellon
School of Computer Science CAPTCHA project..
This reader creates very simple CAPTCHAs from within a Cocoon pipeline,
enabling quick and safe end-user presence identificat. As an example, look at the
following pipeline snippet:
<map:match pattern="*">
<map:read type="captcha" src="{1}"/>
</map:match>
The example will produce an image containing the text in {1}
"warped" or "bent" in a way similar to the Adobe® Photoshop® "Wave"
filter plugin.
Few pipeline parameters control the operation of the
CaptchaReader (this component is not configurable):
width: the width of the image to generate (default: 100).height: the height of the image to generate (default: 50).foreground: the text foreground color (default: random).background: the image background color (default: white).font: the font to use for the text (default: serif).scale: the scaling factor for interim images (default: 5).amount: the amount of text warping to apply (default: 1).quality: the JPEG encoding quality (default: 0.75).
Note that when the foreground 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.
Both the foreground and background parameters accept
strings in the format specified by
Color.decode(String) (for example
fff, or 0099CC) or one of the field names of the
Color class (for example
Color.BLACK BLACK or
Color.cyancyan ...).
The scale 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 with care.
The amount 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.
Remember that in no way the
CaptchaReader claims to be able to
generate "unbreakable" text (that will be impossible), and improvements to the
algorithm are welcome.
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