You ideally want a private camera app that secures/encrypted captured images directly from memory to local storage, digitally signs images with evidenciary chain of control/custody (otherwise, they will not be admissible in a court of law), automatically synchronizes that secured captured images to the cloud (so they are backed up and available on other devices) and of course convenient (ideally free). The picture file should be encrypted by a strong standards based public algorithm, such as 256-BIT AES. The symmetric key used for encrypting the file should be unique per file, and should be protected through asymmetric encryption using the public part of a key pair. Both the private and public portions of the key, should be protected through another derived personal key from something like an account ID and your password (ideally again using well known, proven algorithms such as ones used in WPA2 for wifi). This will emulates a TPM like approach for local key storage, and prevents brute force dictionary attacks on your private keys, while still having the convenience of not only creating private secure pictures, but also viewing them. Here is a YouTube link, describing this approach by an engineer: http://www.youtube.com/watch?v=sh8U7hgwLQg

Simple UI, Mac OX, Windows and iOS support. Good starting point.