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<H2><A NAME="11_1">11.1 Generating Anti-Spam challenge</A></H2>
<P> There are two basic alternatives on how to generate the content of
 the anti-spam image</P>
<OL>
<LI> Submit a string that should be used</LI>
<LI> Automatically generate a random string. If this alternative is
 chosen then the user of the library should save the created string and
 compare it to what the user enters.</LI>
</OL>
<P> In order to write a script to generate a new challenge there are
 four steps to be completed.</P>
<P><B> First</B> include the library file<I> jpgraph_antispam.php</I>.
 Note that there is no need to include the &quot;jpgraph.php&quot; library since
 all functionality is included in this library file.<DIV class="phpscript">
<CODE><FONT color="#000000"> <FONT color="#0000BB">&nbsp;</FONT><FONT color="#007700">
require_once&nbsp;</FONT><FONT color="#DD0000">&quot;jpgraph_antispam.php&quot;</FONT><FONT
color="#007700">;</FONT><FONT color="#0000BB"></FONT></FONT></CODE></DIV>
</P>
<P><B> Secondly</B> a new instance of the class<I> AntiSpam</I> must be
 created<DIV class="phpscript"><CODE><FONT color="#000000"> <FONT color="#0000BB">
&nbsp;$spam&nbsp;</FONT><FONT color="#007700">=&nbsp;new&nbsp;</FONT><FONT color="#0000BB">
AntiSpam</FONT><FONT color="#007700">();</FONT><FONT color="#0000BB"></FONT>
</FONT></CODE></DIV></P>
<P><B> Thirdly</B> the string to be used in the challenge must be
 specified. To automatically generate a suitable string use<DIV class="phpscript">
<CODE><FONT color="#000000"> <FONT color="#0000BB">&nbsp;</FONT><FONT color="#FF8000">
//&nbsp;The&nbsp;argument&nbsp;determines&nbsp;the&nbsp;length&nbsp;of&nbsp;the&nbsp;generated&nbsp;string
<BR></FONT><FONT color="#0000BB">$chars&nbsp;</FONT><FONT color="#007700">=&nbsp;</FONT><FONT
color="#0000BB">$spam</FONT><FONT color="#007700">-&gt;</FONT><FONT color="#0000BB">
Rand</FONT><FONT color="#007700">(</FONT><FONT color="#0000BB">5</FONT><FONT
color="#007700">);</FONT><FONT color="#0000BB"></FONT></FONT></CODE></DIV>
</P>
<P> If instead the string to be used should be specified this string
 should be specified in the initial creation of the AntiSpam() or by
 calling the<I> Set()</I> method as in<DIV class="phpscript"><CODE><FONT color="#000000">
 <FONT color="#0000BB">&nbsp;$spam</FONT><FONT color="#007700">-&gt;</FONT><FONT color="#0000BB">
Set</FONT><FONT color="#007700">(</FONT><FONT color="#DD0000">&quot;aui8k&quot;</FONT><FONT
color="#007700">);</FONT><FONT color="#0000BB"></FONT></FONT></CODE></DIV>
</P>
<P>Please note that in order to minimize the risk for confusion the
 letters 'O' and the number '0' (zero) is not allowed since they are too
 alike and can be mistaken for each other.</P>
<P><B> The final and fourth step</B> is to output the image with a call
 the method<I> Stroke()</I> on the created instance of the<I> AntiSpam</I>
 class.<DIV class="phpscript"><CODE><FONT color="#000000"> <FONT color="#0000BB">
&nbsp;</FONT><FONT color="#007700">if(&nbsp;</FONT><FONT color="#0000BB">$spam</FONT><FONT
color="#007700">-&gt;</FONT><FONT color="#0000BB">Stroke</FONT><FONT color="#007700">
()&nbsp;===&nbsp;</FONT><FONT color="#0000BB">false&nbsp;</FONT><FONT color="#007700">
)&nbsp;{
<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
color="#007700">);
<BR>}</FONT><FONT color="#0000BB"></FONT></FONT></CODE></DIV></P>
<P>Note that we have put a guard around the output since in the case of
 an error this method will result a boolean false value. As with the
 other graph types it is possible to write the generated image to a file
 by submitting a file name as an argument to<I> Stroke()</I>.</P>
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