type
TImageSize = record
Width: Integer;
Height: Integer;
end;

function ReadGIFSize(Stream: TStream): TImageSize;
type
TGifHeader = record
Signature: array [0..5] of Char;
Width, Height: Word;
end;
var
Header: TGifHeader;
begin
FillChar(Header, SizeOf(TGifHeader), #0);
Result.Width := -1;
Result.Height := -1;
with Stream do
begin
Seek(0, soFromBeginning);
ReadBuffer(Header, SizeOf(TGifHeader));
end;
if (AnsiUpperCase(Header.Signature) = ‘GIF89A’) or
(AnsiUpperCase(Header.Signature) = ‘GIF87A’) then
begin
Result.Width := Header.Width;
Result.Height := Header.Height;
end;
end;

procedure TForm1.Button1Click(Sender: TObject);
const
FileName = ‘D:\test.gif’;
var
fs: TFileStream;
gifsize: TImageSize;
begin
fs := TFileStream.Create(FileName, fmOpenRead or fmShareDenyWrite);
try
gifsize := ReadGIFSize(fs);
ShowMessage(Format(’Breite %d Hцhe %d’, [gifsize.Width, gifsize.Height]));
finally
fs.Free;
end;
end;