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  28  <H2><A NAME="12_1">12.1 Generating Anti-Spam challenge</A></H2>
  29  <P> There are two basic alternatives on how to generate the content of
  30   the anti-spam image</P>
  31  <OL>
  32  <LI> Submit a string that should be used</LI>
  33  <LI> Automatically generate a random string. If this alternative is
  34   chosen then the user of the library should save the created string and
  35   compare it to what the user enters.</LI>
  36  </OL>
  37  <P> In order to write a script to generate a new challenge there are
  38   four steps to be completed.</P>
  39  <P><B> First</B> include the library file<I> jpgraph_antispam.php</I>.
  40   Note that there is no need to include the &quot;jpgraph.php&quot; library since
  41   all functionality is included in this library file.<DIV class="phpscript">
  42  <CODE><FONT color="#000000"> <FONT color="#0000BB">&nbsp;</FONT><FONT color="#007700">
  43  require_once&nbsp;</FONT><FONT color="#DD0000">&quot;jpgraph_antispam.php&quot;</FONT><FONT
  44  color="#007700">;</FONT><FONT color="#0000BB"></FONT></FONT></CODE></DIV>
  45  </P>
  46  <P><B> Secondly</B> a new instance of the class<I> AntiSpam</I> must be
  47   created<DIV class="phpscript"><CODE><FONT color="#000000"> <FONT color="#0000BB">
  48  &nbsp;$spam&nbsp;</FONT><FONT color="#007700">=&nbsp;new&nbsp;</FONT><FONT color="#0000BB">
  49  AntiSpam</FONT><FONT color="#007700">();</FONT><FONT color="#0000BB"></FONT>
  50  </FONT></CODE></DIV></P>
  51  <P><B> Thirdly</B> the string to be used in the challenge must be
  52   specified. To automatically generate a suitable string use<DIV class="phpscript">
  53  <CODE><FONT color="#000000"> <FONT color="#0000BB">&nbsp;</FONT><FONT color="#FF8000">
  54  //&nbsp;The&nbsp;argument&nbsp;determines&nbsp;the&nbsp;length&nbsp;of&nbsp;the&nbsp;generated&nbsp;string
  55  <BR></FONT><FONT color="#0000BB">$chars&nbsp;</FONT><FONT color="#007700">=&nbsp;</FONT><FONT
  56  color="#0000BB">$spam</FONT><FONT color="#007700">-&gt;</FONT><FONT color="#0000BB">
  57  Rand</FONT><FONT color="#007700">(</FONT><FONT color="#0000BB">5</FONT><FONT
  58  color="#007700">);</FONT><FONT color="#0000BB"></FONT></FONT></CODE></DIV>
  59  </P>
  60  <P> If instead the string to be used should be specified this string
  61   should be specified in the initial creation of the AntiSpam() or by
  62   calling the<I> Set()</I> method as in<DIV class="phpscript"><CODE><FONT color="#000000">
  63   <FONT color="#0000BB">&nbsp;$spam</FONT><FONT color="#007700">-&gt;</FONT><FONT color="#0000BB">
  64  Set</FONT><FONT color="#007700">(</FONT><FONT color="#DD0000">&quot;aui8k&quot;</FONT><FONT
  65  color="#007700">);</FONT><FONT color="#0000BB"></FONT></FONT></CODE></DIV>
  66  </P>
  67  <P>Please note that in order to minimize the risk for confusion the
  68   letters 'O' and the number '0' (zero) is not allowed since they are too
  69   alike and can be mistaken for each other.</P>
  70  <P><B> The final and fourth step</B> is to output the image with a call
  71   the method<I> Stroke()</I> on the created instance of the<I> AntiSpam</I>
  72   class.<DIV class="phpscript"><CODE><FONT color="#000000"> <FONT color="#0000BB">
  73  &nbsp;</FONT><FONT color="#007700">if(&nbsp;</FONT><FONT color="#0000BB">$spam</FONT><FONT
  74  color="#007700">-&gt;</FONT><FONT color="#0000BB">Stroke</FONT><FONT color="#007700">
  75  ()&nbsp;===&nbsp;</FONT><FONT color="#0000BB">false&nbsp;</FONT><FONT color="#007700">
  76  )&nbsp;{
  77  <BR>&nbsp;&nbsp;&nbsp;&nbsp;die(</FONT><FONT color="#DD0000">&quot;Illegal&nbsp;or&nbsp;no&nbsp;data&nbsp;to&nbsp;plot&quot;</FONT><FONT
  78  color="#007700">);
  79  <BR>}</FONT><FONT color="#0000BB"></FONT></FONT></CODE></DIV></P>
  80  <P>Note that we have put a guard around the output since in the case of
  81   an error this method will result a boolean false value. As with the
  82   other graph types it is possible to write the generated image to a file
  83   by submitting a file name as an argument to<I> Stroke()</I>.</P>
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