The dialog is a part of the Image Scan wizard.
To define a scan area. This dialog is available when Scan w/o Image type was selected in the Scanning: Scan Type Selection dialog.
You can specify three vertices of a rectangular area and the fourth vertice will be computed automatically or four vertices to make an arbitrary four-sided area. The vertices are labeled: Upper Left, Lower Left, Upper Right and Lower Right.
Specify each of 3 or 4 vertices of a scan area:
Click Next to open the Interval dialog.