Compatibility with Suffusion theme

My church’s site at http://www.stmartinschurch.org is not correctly displaying when iThemes Security is active. The header graphic does not display, nor do several other graphics, in Chrome or Firefox (Mac and PC). In Safari, the slider does not display. In all cases, however, it works when I am logged into the admin area.

Do you have any suggestions for how to troubleshoot this? I’m grateful for any suggestions anyone can offer.

https://wordpress.org/plugins/better-wp-security/