function GenerateBMP :TBitmap
var
bmp:TBitmap;
begin
bmp:=TBitmap.Create;
....
result:=bmp
end;

bitmap CreateMyBitmap (char mytxt)
{
	
return bitmap;
}

void __fastcall TForm1::Timer1Timer(TObject *Sender)
{
if (FileExists("inputdata.exchange")){
        Memo1->Lines->LoadFromFile("inputdata.exchange");
        Edit1->Text="/"+Memo1->Text;
        Button1->Click();
        }
}

void BmpImage(int xdim, int ucut, output *out) {
	int i, j, k, l, start, nwords, obt, ebit, sbit, sebit, q = 1;
	FILE *ofile;

	ofile = fopen("resultbmp.bmp","wb");
	BmpHeader(xdim,out,ofile);
.....
.....
	fclose(ofile);
}

image1.picture.assign(myReceivedBitmap)

library testlib;

uses
  Classes, Graphics;

function GenerateBitmap(input:string):Tbitmap;

  function ProcessBitmapCreation:Tbitmap;
  var
  bmp:TBitmap;
  begin
  bmp:=TBitmap.Create;
  bmp.Width:=100;
  bmp.Height:=100;
  bmp.Canvas.Brush.Color:=clGreen;
  bmp.Canvas.Rectangle(100,100,100,100);
  result:=bmp;
  end;
begin
if length(input)>0 then
result:=ProcessBitmapCreation;
end;

exports GenerateBitmap name 'GenerateTestBitmap';
{$R *.res}

begin
end.

function GenerateBitmap(input: string):Tbitmap; stdcall;
  external 'Testlib.dll' name 'GenerateBitmap';

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var
s:string;
begin
s:=edit1.Text;
image1.Picture.Bitmap:=GenerateBitmap(s);
end;

function GenerateBitmap(input: string):Tbitmap; stdcall;
  external 'Testlib.dll' name 'GenerateTestBitmap';