How come the sepia images are blank?
This is most likely due to an older version of ImageMagick. Go to the Admin -> About tab and look for ImageMagick version. The command to create a sepia image was added in either version 6.2.1 or 6.2.2. If you are using a version prior to this sepia toning will not work.
You can either ask your host to upgrade or remove the sepia link from your theme file.