Boot "always clean" from a persistent image

[manzamanna]

Hi all,
I've just installed Knoppix on USB with persistent image.
Now It always saves changes on persistent image at shutdown.
I want to save persistent image only if needed, and boot from it in read only mode, keeping my configuration always clean, can you help me?

[utu]

I enjoy using Knoppix 6.2.1 on a 2Gb USB SD Card.
This is my way of 'dual-booting' my Dell 1545 Window 7 machine.

I keep copies of knoppix-data.img as a 'back-ups' on another
USB card to use if required to restore my working 6.2.1 setup.

I make additional copies from time to time, since I'm always
tinkering with Knoppix. These copies allow me to revert back to
earlier configurations, if necessary, while retaining whatever
changes that continue to serve my purposes.