WPF ProgressBar, how to remove "squares"?

Question

WPF

The application uses the image as an indicator for the ProgressBar.
The problem is the following, on Win 8 everything works as it should and looks like this

But on Win XP or Win 7 in the form of "squares"

How to remove these "squares"?

Answer 1

Part of the ProgressBar style is hardwired into its C# code and there is no way to remove it. For my project, I had to write my own control and style for it. Here is the source code .