Thanks, cclapper, if my first attempt to reach them through the report button doesn't work, I will use the form.
In the present case, I prefered to contact the user first because this watermarked image (from Lucky Oliver) had been in so many places that the person might truly not know the image was copyrighted - the watermark is even a bit faint. In other cases, people removed the image. This person however is insisting in the mistake. Apparently she doesn't even use this blog anymore, as the last post in December she said she would take a break from it. But I suppose she would have received an email saying there was a comment on her blog - or not?