That very much depends how and where you place the "secret", and what other conditions/restrictions are in place. Network storage (such as cloud services or email) e.g. require a network connection to be present, and the transfer might be noticed. A local copy might not have the copy-process noticed, but the copies could be found, in most times easily when using a file explorer. Your "secret act" might also indicate infringment on a 3rd persons privacy (if only your own photos are involved, then why the secrecy?), which not only would be indecent, but also may incur a penalty (no accusing, just a hint).
But assuming completely legal application, there might be a few options available:
- photoCopy backups photos to email. The app's description states: "when the program runs, there is no indication at all"
- Photo Auto Uploader automatically uploads pictures to Picasa or Facebook after pictures are captured
- Auto Uploader does the same for configured services
- FolderSync can synchronize your photo's folder (and of course others) periodically in the background -- to cloud services as well as to your home computer
There are more apps for each of the mentioned categories. There may also be some to create local copies, but I'm not aware of any at this time.