These two settings look ok - check also that php setting allow_url_fopen is on...
One possible reason might then be that some security module (SeLinux?) could block the creation process of mimetex images - file permissions look correct too.
In some rare cases some "other reason" can corrupt files or commands - for example if config.php is saved as utf-8 encoded file with BOM it may corrupt all images (should be saved as ANSI file) - or some extra .htaccess file in a wrong place - but it is hard to guess such things...