It may be that the tiny craft is simply too small for the camera to spot, and will remain lost in space until higher resolution imagery of Mars is available.
Rapiscan Systems, which makes the backscatter X-ray scanner, installs one of a series of "privacy algorithms" that can dial up or down the images' resolution. (Of course, the fuzzier the result the harder it is to spot a weapon.) Similarly, millimeter scanner-maker L-3 can blur faces, chests and groins, depending on the customer's preference.