Private images also viewable even no login

At my site private marked  pictures are also viewable to any user. I am not sure, it a bug of dolphin or some miss configuration.

Please checkout.

Looks to me its not the actual private picture, just the usual placeholder which has been changed by your template etc.

Thank you for reply. Please, can you help me how to remove this?

I don't see a reference to the Dolphin version.