The images are PNG (screenshots). Sample image sizes are 755x511, 580x347, 748x536, 335x474 and 692x508. I'm printing to an A4 page with image resolution set to the default of 96 dpi.
I'm viewing the PDF in Preview on OS X 10.7. PDF file is generated on OS X.
I have generated PDF files with Prince and my current PDF solution using the same source materials. The images look fine in the PDF created with my current solution. They are blurry with Prince. What I'm seeing looks very similar to what I saw with a PDF library I used to use (prior to feature that coerced coordinates/dimensions to integers). I can provide source material along with the output I'm getting on my end if that would be helpful.
Blue Mango Learning Systems
http://www.screensteps.com - http://www.clarify-it.com