It's a touch screen I'm working with, so, if someone knocks it accidently they would be clicking on the picture and a password form appears. I'd rather this not happen. So I was going to place an invisable button in the top left hand corner. If you know where the button is you'll click it easily but there's less chance of someone who doesn't know about it accidently clicking it. I'm developing in windows forms.
PS I said a picture, it's a webpage that I'm showing (sorry) don't know if it makes any differences