Here is what I thing needs to be done to help with spam registers, The problems lays with in to two things
one the email and 2 when you create the custom register the options are two limited, Here is what I think needs to be done
one there needs to be a verify email that a lot of company's used where a email is sent first and must be verified if the email is not verified with in 24 hours the account is automatically deleted, Next something should be sit up so only certain emails can be used that are verified email company's such as gmail hotmail outlook.
In the custom register section you should have the option drop down boxs or questions and also have a upload feature these options should have the option to be made mandatory I believe these will help with the spam bots