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use artichow or jgraph they r open source just download it and customize it according to your need

// To send HTML mail, the Content-type header must be set

$headers = 'MIME-Version: 1.0' . "\r\n";
$headers .= 'Content-type: text/html; charset=iso-8859-1' . "\r\n";

// Additional headers...

or simply use this

$pass = md5(uniqid(rand(), true));