Firstly run a piece of white cardstock through the Big Shot using the Top Note Die. Discard the centre piece & keep the outer frame.
Stick the top edge of the frame to the die using cellotape.
Place your photo or whatever it is you want to centre under the frame and adjust it until you are happy with the position.
Run the 'sandwich' back through the Big Shot & voila you are left with a perfectly cut picture exactly as you want it.
I hope you have found this useful.