unfortunately nobody here is responsible for what purpose FlatPress is being used.
As the main creator of FlatPress, while I'm very disappointed to hear such a thing, my only suggestion can be to either try and contact the owner of this website and kindly ask to pull down the pictures;
if there is no obvious way to contact him, there is always a /contact.php page you can try to reach; I have some doubts it would work.
you can also try to whois (e.g. http://www.whois.net/ ) his/her domain to know who's the owner (usually there is an email filed). You can also contact his/her web host and demand to pull down the images on behalf of the owner, or demand to shut the site down, if he/she is violating their TOS.
If everything else fails, you have the right to take legal action.