>usually the Perl module has to be installed separately
Sorry, I meant that the Perl module comes with installing ImageMagick itself if you do it from source. From my experience installing it from source is straightforward (they make it so necessarily). Just a thought I wanted to mention since I've use gone down a similar route with image manipulation. I didn't do any shrinking, but added some watermarks to images I was serving. I also served up different "sizes". But it was all done via the Perl library, not convert itself. Anyway, I think your use of Perl is really neat here.