Today's Image of Mars comes from HiRISE and shows a possible future landing site in Antoniadi Crater, a 394km long crater on Syrtis Major Planum. It is evidenced that Antoniadi Crater once had rivers and lakes, as evidenced by the inverted features, like riverbeds.
Inverted features are formed when the sediment deposited by water is harder than the surrounding terrain. Over billions of years erosion wore down the surrounding terrain, but because the lake and riverbeds were more resistant to erosion they were reduced much less, thus creating inverted features.
The fact that there was once flowing water in Antoniadi Crater makes it a prime target for future missions to Mars. This particular patch shows a particular candidate landing site in the crater. It was chosen because it has been observed to have relatively flat terrain and is close to features of interest.
Clicking on this image will take you to other showcased images of potential landing sites for future missions to Mars because HiRISE has not yet provided a caption for this image. [EDIT 24 June 2012: HiRISE has added a caption.]