[]
You can restrict the portion of a window's client area you want to display in the thumbnail preview by setting the ClipControl property to the ID of one of the form's elements.
To restrict the thumbnail image to one element of your form, set the ClipControl property to the ID of that element. For example:
To write code in Visual Basic
C1TaskbarButton1.Thumbnail.ClipControl = button1
To write code in C#
c1TaskbarButton1.Thumbnail.ClipControl = button1;