If you use Vignette to take your photo - then the 'original' shot is however you process it in Vignette
if you import the shot from the camera in to Vignette then you still retain the original shot (camera shot will be in the default camera app directory while the Vignette photo will be saved in the vignette folder)
That being said - you can decide to not have Vignette do any effects or processing on the photo and it does give you the option to save a copy - meaning it saves what you took - but doesn't exit out of the app - allowing you to then go on to playing with the frames/effects. This is particularly handy if you want to save multiple versions of the same shot without having to keep importing the shot back in to the app.
Which was handy when I was writing my review of the app and making samples