Your Crop needs the equivalent of +repage in order to shrink the canvas. I think your Set should be 
$background->Set( page=>'0x0+0+0' );

[download]
to get around the fact that perlmagic (at least in the version I've most recently used) has no repage.

In reply to Re: Image::Magick keeps dimensions of loaded file by traveler
in thread Image::Magick keeps dimensions of loaded file by cowgirl

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