This image was shot by the High Resolution Stereo Camera (HRSC) of spacecraft Mars Express. It shows Mars' South Pole during winter, when an extra layer of frozen CO2 (dry ice) covers the permanent ice cap. This permanent ice cap is located in the centre of the image and - like here on Earth - mainly consists of water ice. However, temperatures at Mars' South Pole can drop to -153 °C (-243 °F), considerably below the lowest temperatures at Earth's South Pole (-82 °C or -116 °F) and low enough to make CO2 freeze. Over the course of one Mars year, up to one quarter of Mars' atmosphere (which consists of 96% carbon dioxide) can be bound to the poles in the form of dry ice. When winter ends at Mars’ South Pole the frozen carbon dioxide sublimates into gas again and the permanent water ice caps appear again. This sublimation can cause unpleasant winds with speeds of up to 400 km/h (250 mph).
The amount of water ice stored in the permanent ice cap is considerable: the ice layers are up to 4 km thick. If you were to melt all the water ice at the South Pole the whole of planet Mars would be covered by a water ocean 11 metres deep!