How do I make the picture shrink to page size?

I want my picture to fit into the page when viewed in IE.
If I just view the picture on its own, I get the "Expand to
normal size" button at the bottom right corner, but when
its an html page I don't.
Tia.

It does work, but not in my own html page, i.e. it works in other
sites in general. Is there something I need to add to the img tag?

It's not a browser problem. I clearly remember visiting websites
where I needed to press the button in the bottom right, but
for my website it doesn't work. It is nothing to do with this option
in IE, which was btw enables, since as I said before when I view an image in
IE i.e. just double clicking on it from the desktop, it will do it.