[NumLock]

или сразу так:

Код:

var
  doc: IHTMLDocument2;
  i: Integer;
  img: IHTMLImgElement;
begin
  doc:=WebBrowser1.Document as IHTMLDocument2;
  for i:=0 to doc.all.length-1 do
    if doc.all.item(i, 0).QueryInterface(IID_IHTMLImgElement, img)=S_OK then
      ShowMessage(IntToStr(img.width));
end;