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 Guide
The User Interface
Customize the Drawing Environment
Set 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.