According to the documentation, Mail::Pop3Client::Retrieve gives you the head and body of an email message, and Mail::Message::Attachment::Stripper expects a Mail::Message object in it's constructor.
You could try taking the $msg you get from Retrieve and constructing/building a Mail::Message object, like so:
You know, I started reading through the documentation but realized it would take me a bit more time to fully understand it, and extract the bits I would need in order to help you with your task.
I will recommend instead that you read the associated documentation that I have referenced above, and take the hints I allude to above (construct, build) to find the relevant documentation for your task of converting your message into a Mail::Messsage object. Otherwise, I would be inclined to use something I'm a bit more familiar with (or at least can state that I've used it before ;-) and give you a link for another way to carry out your task using Mime::Parser, with working code that strips jpeg attachments off of emails, though not coming through pop3 interface. That was written a long time ago, when I was first learning Mime::Parser, and thus has TONS of debugging output littered through the code. Perhaps this approach will be easier for you?
s**lil*; $*=join'',sort split q**; s;.*;grr; &&s+(.(.)).+$2$1+; $; =
qq-$_-;s,.*,ahc,;$,.=chop for split q,,,reverse;print for($,,$;,$*,$/)