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<HR NOSHADE>
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<H1><A NAME="11">11 Anti-Spam Challenges</A></H1>
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<P> JpGraph includes a module to easily generate Anti-Spam challenges.
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With this we mean an image consisting of numbers and letters which are
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very hard to read for an OCR program. This is often used to secure sign
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up for bulletin boards, on-line mail system or mailing lists since this
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very effectively prevent automatic sign up by robots (spam-bots).</P>
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<P> The module in JpGraph responsible for this is<I>
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jpgraph_antispam.php</I> and behaves as a simplified plot module.</P>
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<P> The example below illustrates how such an image can look like<DIV class="example">
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<BR> <A href="exframes/frame_antispamex01.html" target="blank"><IMG border="0"
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HEIGHT="34" src="img/img/img/img/img/img/antispamex01.png" WIDTH="101"></A>
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<BR><B>Figure 195:</B> Simple illustration of spam challenge image <A href="exframes/frame_antispamex01.html"
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target="blank">[src]</A>
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<P></P>
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<P>Anti spam images have less functionality then the usual images
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generated with JpGraph in order to keep this utility reasonable small.
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The primary limitation is that there are now additional formatting
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options for the images and the image generated will always use the<I>
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JPEG</I> image format. Hence it is not possible to change this to use,
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for example, PNG.</P>
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