Take a look at Daniel Kasak's PDF::ReportWriter and examples. I worked heavily on it, and it can do amazing things, like template PDF pages, gif/jpg/png images, barcodes, and it's XML driven.

Look at the template feature: you can use an existing PDF file as background (put your image in a PDF, for example) and start writing on it.

You can check out the code to see how it's implemented (some cool PDF::API2 use)...