bild_bmp BITMAP "bmp.bmp"
bild_jpg RCDATA "jpg.jpg"
bild_png RCDATA "png.png"
bild_gif RCDATA "gif.gif"

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.ExtCtrls, Vcl.StdCtrls, JPEG, PNGImage, GIFImg;

...

function GetGraphicFromResource(Name: String): TGraphic;
var
  RS: TResourceStream;
  ImageBMP : TBitmap;
  ImageJPG : TJPEGImage;
  ImagePNG : TPNGImage;
  ImageGif : TGIFImage;
  FileExtension : String;
  Graphic : TGraphic;
begin
  FileExtension := LowerCase(Copy(Name, Length(Name)-2, 3));

  Graphic := TGraphic.Create;
  Graphic := nil;

  RS := TResourceStream.Create(hInstance, Name, RT_RCDATA);
  try

    if FileExtension = LowerCase('bmp') then
    begin
      ImageBMP := TBitmap.Create;
      try
        ImageBMP.LoadFromStream(RS);
        Graphic := ImageBMP;
      finally
        ImageBMP.Free;
      end;
    end;

    if FileExtension = LowerCase('jpg') then
    begin
      ImageJPG := TJPEGImage.Create;
      try
        ImageJPG.LoadFromStream(RS);
        Graphic := ImageJPG;
      finally
        ImageJPG.Free;
      end;
    end;

    if FileExtension = LowerCase('jpeg') then
    begin
      ImageJPG := TJPEGImage.Create;
      try
        ImageJPG.LoadFromStream(RS);
        Graphic := ImageJPG;
      finally
        ImageJPG.Free;
      end;
    end;

    if FileExtension = LowerCase('png') then
    begin
      ImagePNG := TPNGImage.Create;
      try
        ImagePNG.LoadFromStream(RS);
        Graphic := ImagePNG;
      finally
        ImagePNG.Free;
      end;
    end;

    if FileExtension = LowerCase('gif') then
    begin
      ImageGif := TGIFImage.Create;
      try
        ImageGif.LoadFromStream(RS);
        Graphic := ImageGif;
      finally
        ImageGif.Free;
      end;
    end;
  finally
    RS.Free;
  end;

  if Graphic <> nil then
  begin
    showmessage('gr vorhanden');
    //Form1.image1.Picture.Graphic := graphic;

    //showmessage('gr vorhanden');
    Result := Graphic;
  end;
end;

procedure TForm1.Button5Click(Sender: TObject);
begin
  image1.Picture.Graphic := nil;
  image1.Picture.Graphic := (GetGraphicFromResource('bild_jpg'));
  //image1.Picture.Graphic.Assign(GetGraphicFromResource('bild_jpg'));
end;