Get width and height of GIF/JPG images stored as arrays of bytes.
Optimized to use within server apps.

function GetJpegSize(a: array of byte; var width, height: integer): boolean;
var
  i, n: integer;
begin
  n := length(a) - 8;
  i := 1;
  while (i < n) and (a[i] = $FF) do //Loop arround JPEG blocks
    case a[i + 1] of
      $C0 .. $C3: //Goal block
        begin
          height := a[i + 5] * 256 + a[i + 6];
          width := a[i + 7] * 256 + a[i + 8];
          Result := True;
          exit;
        end;
      $FF: //Nop block
        inc(i);
      $D0 .. $D9, $01: //Info block
        inc(i, 2);
      else //Normal block
        inc(i, a[i + 2] * 256 + a[i + 3] + 2);
    end;
  Result := False;
end;

function GetGifSize(a: array of byte; var width, height: integer): boolean;
begin
  Result := (a[1] = $47) and (a[2] = $49) and (a[3] = $46); //'GIF' Signature
  width := a[8] * 256 + a[7];
  height := a[10] * 256 + a[9];
end;


Functions return False if file is corrupted.

Usage:

var
  f: file;
  i, x, y: integer;
  a: array of byte;
begin
  assignfile(f, YOUR_GIF_FILENAME);
  reset(f, 1);
  i := filesize(f);
  setlength(a, i);
  blockread(f, a[1], i);
  if GetGIFSize(a, x, y) then
    writeln('Width ', x, ' Height ',y)
  else
    writeln('Error');
  closefile(f);
  readln;
end.