How to filter multiple image attachments?

I'm trying to figure out how to filter spam where the message is  
nothing but a bunch of image attachments.  I haven't figured out a  
way to filter spam that's just a single image, but when it's a jigsaw  
of several images I figure I can check to see if the messages  
contains multiple images.  But I don't know a regexp that will do  
that.  I couldn't find syntax for matching something, say, 10 or more  
times.  I think the following works in Perl but it didn't seem to  
work in Procmail:

        :0 B
        * (_NextPart.+){10,}
        !filterbox(_at_)mydomain(_dot_)com



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