<?php include ($mosConfig_absolute_path.'/administrator/components/com_securityimages/client.php'); ?>
<?php echo insertSecurityImage("security_refid"); ?>
<?php echo getSecurityImageText("security_try"); ?>
<?php echo getSecurityImageTextHeader(); ?> 
<?php echo getSecurityImageTextHelp(); ?>
<?php echo getSecurityImageField("security_try"); ?>  

The code above insert the image, and the text,
You page normally submit information to the server for processing.
Most of the time, the last 2 lines are inserted in a <form>

include ($mosConfig_absolute_path.'/administrator/components/com_securityimages/server.php');

$checkSecurity = checkSecurityImage($security_refid, $security_try);

if $checkSecurity = true //then the user has entered the right text.