How can I tell the resolution of scanned PDF from within a shell script?

Question

I have a large collection of documents scanned into PDF format, and I wish to write a shell script that will convert each document to DjVu format. Some documents were scanned a

Answer 1

Apago's PDF Spy will tell you the acutal resolution of images in a PDF along with lots of other stuff. It's a commercial product but has a 10 day demo.