If you do not specify a path to the image, AutoCAD Raster Design toolset searches for the image using the Project Files Search Path configured in the AutoCAD Preferences dialog box. For more information, open the main Help window for Autodesk Civil 3D, then select AutoCAD HelpUser’s GuideThe User InterfaceCustomize the Drawing EnvironmentSet Interface Options.
AutoCAD Raster Design toolset searches for the image in the path that you specify. If AutoCAD Raster Design toolset cannot locate the image in this path, it searches for the image using the AutoCAD Project Files Search Path.