Mephistopheles

It sounds like one of the conditions in the if statement might be evaluating to false. Can you try printing the output of each condition individually to see what they evaluate to?

You could try setting the cache headers directly as part of the script where the existing Content-Type header is being set.

$mysidia = Registry::get("mysidia");
header('Content-type: image/png');

// add these
$cache_for = 2419200; // One month in seconds 
$cache_until = gmdate("D, d M Y H:i:s", time() + $cache_for) . " GMT";
header("Expires: $cache_until");
header("Cache-Control: max-age=$cache_for");

I checked the file over and it seemed fine to me - the problem might lie somewhere else.

Do you want to try a clean local install of the script?

Has AppController been modified at all? Would you be able to post a copy here? There might be an extraneous semi-colon or something in AppController causing the error message to appear. (I am assuming you just copied everything from the online server to your local one.)

Please post your config.php file and remove any database credentials or other sensitive information. I suspect your SCRIPTPATH config variable is set incorrectly.

These two lines don't match:

/home/vol8_8/epizy.com/epiz_26559584/htdocs/home/vol8_8/epizy.com/epiz_26559584/htdocs/adopt//inc/smarty/Smarty.class.php'

/home/vol8_8/epizy.com/epiz_26559584/htdocs/adopt/classes/class_mysidia.php

They need to match in order to work.

Is there any particular reason you chose Unity for this?

You can embed Unity into a webpage, so your creature generator should still run, but there are alternatives like standard programming languages (PHP, Node, Ruby, etc.) which can do the same thing.