The access rights are stored as bits of 64bit value and the maximum number of different rights cannot exceed 64. ImageGear predefines some list of access rights that can be extended. If you need to extend the list of access rights, you have to create a new class and inherit it from ImGearARTAccessRights, where you can define your own rights. The bits from 0 to 31 are reserved by ImageGear and must not be used to define the custom rights. For the custom defined rights, use bits from 32 to 63.

Reference

ImGearARTAccessRights Members
ImageGear.ART Namespace