How to get the current directory?

I have many files in directory "image", the filenames has been saved in database. Before I use file, I want to know, that this file exists.
So I use System.IO.File.Exists("image/"+filename), but it returns false (also, when "../image/" etc.)
 I want to retrieve a directory root, so I use System.IO.Directory.GetCurrentDirectory - but as result I have
C:\Program Files\Microsoft Visual Studio 8\Common7\IDE So it is directory for Visual Studio, but not with my site.  
What can I find a directory with my site?
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