SD cards have a physical switch to write-protect them, but the logic & protection is done in software.
For example, there's a project that provides replacement firmware for Canon cameras - http://chdk.wikia.com/wiki/CHDK - stored on the SD card. The new firmware is selected by moving the write-protect switch on the card. In either configuration, the camera can still save new photos to the storage.
For example, there's a project that provides replacement firmware for Canon cameras - http://chdk.wikia.com/wiki/CHDK - stored on the SD card. The new firmware is selected by moving the write-protect switch on the card. In either configuration, the camera can still save new photos to the storage.