This is caused by the images not using absolute URLs. When you use SEF URLs, all the images on the website need to use absolute URLs, otherwise they cannot be loaded correctly by the browser. You can probably fix the background image and logo in your website's template (just make the URLs absolute), but if there is also problem on JomSocial page, that means that the component does not support SEF URLs correctly. Unfortunately, there's not much that JoomSEF can do about this at the moment - you can only try some other setting for the "Set page base href value" option, but I'm afraid that none of them will work for both the login and images.
You should probably contact the developers of components that are causing problems to make the images URLs absolute directly in their code. Or we can fix the components for you, but that would be paid support service and the price would depend on the time it would take us - see
www.artio.net/e-shop/support-services
Best regards,
ARTIO Support Team