A couple of things come to mind;
Originally Posted by kayrode
1. The materials your cameras are made from may not be opaque enough. The paper seems pretty uniformly fogged.
2. Is the paper good to start with? Was it loaded properly? To check if the paper is still good, I'd process an unexposed sheet to verify.
3. What's your exposure time? It's possible that you have more than one thing going wrong (i.e., camera leaks light coupled with not enough or too much exposure).
4. I'd also check your pinhole size. Optimal pinhole size will vary depending on the size of your recording media (paper or film) and the desired focal length.