Always get wrong path!!??

The problem is imho not the use of GetFullPath, but the things you're doing with it.

So can you post a concise and complete example (source).

Some hints:

Don't use relative paths at all. When the data in the imag folder is user specific, then store it below %USERPROFILE%. When it's user data for all users on the machine, then store it in %PROGRAMDATA%. Store it only in a folder below the executable, when it is static data. But consider in the last case to use embedded resources.