create Rectangle by user and save its Relative position

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VB

WPF

WPF-Toolkit

Hi,

First of all - I need my project to be in WPF .. and it's my first one.
(I mostly develop web systems)

I have a form with a grid in it, that split the window to 2 rows / 1 column.
On the second row I added a canvan with a background image that display several items and there's a barcode below each item.

When a user (from group "a") search a barcode on the image, it suppose to be marked, so as a start, other group of users ("manager" group) need to set the image details and this is the part I'm having problem with

what I need to do is that:

The user that opens the window, suppose to be able to create a rectangle that marks a barcode of an item.
He also suppose to be able to change the width/height of the rectangle.
After he finishs, by clicking a button I want to save the relative position of the rectangle on the window - it must be a relative position, since the user (from group "a") can change later the window height/width and the rectangle needs to stay at the same place on the image...

Can anyone give me a start point or any kind of help?