I was wondering how we may apply secure computing (e.g. computation over encrypted data) in real life scenarios where you have to interact with real objects as opposed to bits and bytes. It seems to me quite difficult, if not impossible, to achieve the same "invisibility" in the physical world; the very nature of the tangibility makes it hard to do so.
Consider the example where I want to mail my digital photos to Walgreens and get them printed. However, I want Walgreens to see neither the photos nor the printed copies. You see the similar privacy/security problems in getting something printed through a courier service such as UPS. I am not aware of any technology that we could use to solve this problem. One important thing is for the solution to be economical for me (the service requester), the amount of work I need to do (hence the cost) to recover the actual thing (actual photos from printed copies) should be cheaper than the service I want (getting the photos printed) in the long run. Otherwise, I might as well buy my own printing machine and do the printing myself which will eliminate the problem of privacy/security.