将图片压缩后转Base64函数

function CutImgToBase(fn: string): string;  // 压缩图片只能压缩bmp：将jpg转换成bmp再压缩
var
	m1: TMemoryStream;
	m2: TStringStream;
	jpg: TJPEGImage;
	bmp: TBitmap;
begin
	jpg := TJpegImage.Create;
	bmp := TBitmap.Create;
  m1 := TMemoryStream.Create;
  m2 := TStringStream.Create;
	jpg.LoadFromFile(fn);
	bmp.Width := jpg.Width div 2;
	bmp.Height := jpg.Height div 2;
	bmp.Canvas.StretchDraw(bmp.Canvas.ClipRect, jpg);
	jpg.Assign(bmp);
	jpg.CompressionQuality := 30;
	jpg.Compress;										// 先指定大小再压缩
	jpg.SaveToStream(m1);
	m1.Position := 0;               // 一定要还原指针，才能base64
	EncdDecd.EncodeStream(m1, m2);
	result := m2.DataString.Replace(#13, '').Replace(#10, '');
	bmp.Free;
	jpg.Free;
  m1.Free;
	m2.Free;
end;

 调用函数：

procedure TForm2.Button4Click(Sender: TObject);   // 调用函数  压缩并编码
var
	m: TStringStream;
	s: string;
begin
	s := CutImgToBase('test.jpg');
	FilePutContents('mm.txt', s);
	m := TStringStream.Create(s);
	Memo1.Lines.Add(m.DataString);
	m.SaveToFile('base64.txt'); 
end;

解码Base64测试：

procedure TForm2.DecodeBaseClick(Sender: TObject);   // 解码
var
	m1: TStringStream;
	m2: TMemoryStream;
begin
	m1 := TStringStream.Create;
	m2 := TMemoryStream.Create;
	m1.LoadFromFile('base64.txt');
	EncdDecd.DecodeStream(m1, m2);
	m2.SaveToFile('1.jpg');
	m1.Free;
	m2.Free;
end;