MS-Windows: take a picture from the webcam

Dear Tcl/Tk developpers,
I have a MS-Windows Tablet with 2 cameras (front/back).
I want to read a QR-code using the cameras.
And the user should be guided by a picture while scanning.
What I need from Tk:
- select a camera
- take a picture (tk image ?)
- show it to the user (Tk label with an image ?) (probably scaled down)
- start the barcode decoder and get the information bc/no bc
- if no bc, get the next picture
- abort by an abort button
Does anybody has an idea for Tk for this ?
Thank you for any answer,
Harald