Broken Admin Panel after SUPEE-8788

After the installation of patch SUPEE-8788 in Magento 1.9.0.1 I have experienced a broken product edit form in Catalog > Manage Products > { select any product } > Edit Product. Every time when I tried to edit a product it was logging the following error message.

I have found a community extension in my project which was causing the problem by rewriting the complete class Mage_Catalog_Helper_Image. With diff I was able to identify all changes which I needed to copy from core to the community extension.

I just added the missing constant

and updated the method validateUploadFile().