The oik-nivo-slider plugin supports scaling of images to fit the space available.
This means that you no longer need to ensure that the images are all the same size.
The images displayed in this slider have different widths (800, 900 and 1000 pixels and different heights)
when the slider is displayed they get scaled up or down to fit horizontally, the slider adjusts its height to cater for the aspect ratio of the image.
Use a responsive theme; theme=default, bar, dark, light or oik