Take a look at pdfimages. Here is the description from the page:
Pdfimages saves images from a Portable
Document Format (PDF) file as
Portable Pixmap (PPM), Portable Bitmap
(PBM), or JPEG files.
Pdfimages reads the PDF file, scans
one or more pages, PDF-file, and
writes one PPM, PBM, or JPEG file for
each image, image-root-nnn.xxx,
where nnn is the image number and
xxx is the image type (.ppm, .pbm,
.jpg).
NB: pdfimages extracts the raw image
data from the PDF file, without
performing any additional
transforms. Any rotation, clipping,
color inversion, etc. done by the PDF
content stream is ignored.