Make an image to fit its parent dimensions

I might be naive, but isn't this as simple as this ?

img {
    width:100%;
    height:100%;
}

The css property that you want is max-width :

Css

img {
    max-width:100%;
}

You could add a container around your image and set overflow:hidden to prevent images to get bigger than the defined width/height.

Use this bit of css to scale your image:

img {
    max-width: 100%;
    max-height: 100%;
}