procedure TForm1.Button1Click(Sender: TObject);
var
bmp:TBitmap;
bf:BLENDFUNCTION;
begin
bmp:=TBitmap.Create;
try
bmp.LoadFromFile('d:\1.bmp');
bf.BlendOp:=AC_SRC_OVER;
bf.BlendFlags:=0;
bf.SourceConstantAlpha:=100;//величина прозрачности (0-255)
bf.AlphaFormat:=0;
Windows.AlphaBlend(Image1.Canvas.Handle, 0, 0, Image1.ClientWidth, Image1.ClientHeight,
bmp.Canvas.Handle, 0, 0, bmp.Width, bmp.Height, bf);
finally
bmp.Free;
end;
end;