If you have Adobe, then go to:

http://ict.cas.psu.edu/training/howto/util/pdf_extract_graphics_v6.htm

It explains how to extract an image or images.

If you have xpdf, then see the man pages for pdfimages and xpdfrc. Pdfimages will extract images, then I would recommend PDF::Create to rebundle your images. Darren's suggestion that you use CAM::PDF works too.