For my program, Path.GetDirectoryName (Assembly.GetExecutingAssembly().Location)
returns
C:\code\test\Junk\bin\Debug
.
cell.Value = Image.FromFile(
Path.Combine (
Path.GetDirectoryName (Assembly.GetExecutingAssembly().Location),
"Resources/warning_Icon"));
Of course, usually you would embed the resources in your assembly unless you want to change them without a recompile.