The bright-looking surface material in the center, where the image is partly overexposed, may not be inherently brighter than the foreground material in shadow. But the scientists are calling this area "Holy Cow." Reportedly (via Emily at the Planetary Society) that's exactly the phrase exclaimed when this image was returned. More pictures of this feature will be imaged using different exposures in an effort to determine if this really is ice.
The other interesting aspect of this image is that the retrorocket nozzles are visible right at the top of the image.
We'll keep you posted when there's more information and data available on the area under the lander.