NB: This function expects the full server-related pathname to work.
For example, if you run a PHP routine from within, for example, the root folder of your website and and ask:
$bstr = file_exists("/images/Proofreading_patients.jpg");
You will get FALSE even if that file does exist off root.
You need to add
$bstr = file_exists(__DIR_."/images/Proofreading_patients.jpg");
to get it to return TRUE - ie : /srv/www/mywebsite.com/public/images/Proofreading_patients.jpg