gecko supports decreasing the size of images to fit the screen size by simply clicking on the image. Would be nice if webkit would support that too ;)
(Of course this is only for plain images, not images embedded into websites)
This is for the GTK port, not sure if it also affects other ports (ideally they should all behave the same and this should be implemented a single time)
Midori supports this, so maybe instead of putting this functionality in Webkit it might be a better idea to put it in the applications?