Tue Oct 14, 2014 7:01 pm
Short answer: NO.
Explanation: An RPi can only boot from an SD card. The SD card reader on a Model B does not detect the read-only tag. (As far as I can see a microSD card does not have a read-only tag, so the B+ can't possibly detect one.)
Longer answer: Sort of, but...
Explanation: An RPi can only boot from an SD card. Once it has been booted control can be passed to a root filesystem on some other device - a USB stick or an external hard drive. The subject of whether Raspbian can be configured to run from a read-only root filesystem has been extensively discussed in the past, and I suggest you search for those discussions. I think the conclusion is that it can be done, with partial success, but it isn't trivial.