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  28  <H2><A NAME="4_2">4.2 How to generate images with PHP</A></H2>
  29  <P> As a general rule each PHP script which generates an image must be
  30   specified in a separate file which is then called in an HTML &lt;IMG&gt; tag.
  31   For example, the following HTML excerpt includes the image generated by
  32   the PHP script in &quot;fig1.php&quot;.</P>
  33  <P><DIV class="phpscript"><CODE><FONT color="#000000"> <FONT color="#0000BB">
  34  &nbsp;</FONT><FONT color="#007700">&lt;</FONT><FONT color="#0000BB">img&nbsp;src</FONT><FONT
  35  color="#007700">=</FONT><FONT color="#DD0000">&quot;fig1.php&quot;&nbsp;</FONT><FONT color="#0000BB">
  36  border</FONT><FONT color="#007700">=</FONT><FONT color="#0000BB">0&nbsp;align</FONT><FONT
  37  color="#007700">=</FONT><FONT color="#0000BB">center&nbsp;width</FONT><FONT color="#007700">
  38  =</FONT><FONT color="#0000BB">300&nbsp;height</FONT><FONT color="#007700">=</FONT><FONT
  39  color="#0000BB">200</FONT><FONT color="#007700">&gt;</FONT><FONT color="#0000BB">
  40  </FONT></FONT></CODE></DIV></P>
  41  <P></P>
  42  <P> Strictly speaking the &quot;align&quot;, &quot;width&quot; and &quot;height&quot; are not
  43   necessary but helps the browser position the image correctly before the
  44   image has been fully sent back to the browser.</P>
  45  <P> The library will automatically generate the necessary headers to be
  46   sent back to the browser so that it correctly recognize the data stream
  47   received as an image of either PNG/GIF/JPEG format. The browser can
  48   then correctly decode the image</P>
  49  <P> Observe that you<STRONG> can't</STRONG> return anything else than an
  50   image from the image script. By definition each HTML page (or more
  51   correctly each HTTP stream) can only consist of one mime type which is
  52   determined by the header for that particular stream.</P>
  53  <P> A common mistake is to have a space in the beginning of the image
  54   script which the HTTP server will send back to the browser. The browser
  55   now assumes that the data coming back from this script is text since it
  56   hasn't received an explicit header. When then the image headers get
  57   sent back to the browser to forewarn the browser of the forthcoming
  58   image the browser will not like that as it has already assumed the data
  59   stream was a text stream. The browser will then give the infamous
  60   &quot;Headers already sent error&quot;.</P>
  61  <P> To include several images together with text on a page you need to
  62   have a parent page with several &lt;IMG&gt; tags which each refers to an
  63   image script (or the same image script with GET/POST data).</P>
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