You will have to pay something. Write back to them tell them that you are sorry ect ect, not your fault someone designed it 3 months ago ect ect and offer them a good will gesture. Tell them the photos have been removed from your site and again you are sorry.
My friend had this and he ended up paying around £300-£500, from a £2000 original bill.
If you are with the FSB, ring and speak to the solictor.