User can set his own file IO functions used when loading from/saving to files by this function.

procedure SetUserFileIO(OpenReadProc: TOpenReadProc; 
                        OpenWriteProc: TOpenWriteProc; 
                        CloseProc: TCloseProc; 
                        EofProc: TEofProc; 
                        SeekProc: TSeekProc; 
                        TellProc: TTellProc; 
                        ReadProc: TReadProc; 
                        WriteProc: TWriteProc);

Imaging (at line 313)