The -draft option removes bitmap (photographic) images from a file, so that it can be printed with less ink. Optionally, the -boxes option can be added, filling the spaces left blank with a crossed box denoting where the image was. This is not guaranteed to be fully visible in all cases (the bitmap may be have been partially covered by vector objects or clipped in the original). For example:
cpdf -draft -boxes in.pdf -o out.pdf