hi,
It's in the file_pluginfile() function in lib/filelib.php - see http://xref-diff.mukudu-dev.net/moodle39/lib/filelib.php.source.html#l4289. But like I said not usually a good idea to core hack but if you must, you might want to check that the file is an image file and set the headers as required just for those files.
It's in the file_pluginfile() function in lib/filelib.php - see http://xref-diff.mukudu-dev.net/moodle39/lib/filelib.php.source.html#l4289. But like I said not usually a good idea to core hack but if you must, you might want to check that the file is an image file and set the headers as required just for those files.