Those pictures you see aren't pictures of aliens and they are not prints that show that aliens have been through. In 1976 the Face on Mars picture was taken, but when it was taken the camera was through some clouds, so when it took the picture it was probably some shadow of the clouds. It even says the when this picture was taken it was a cloudy day "it was winter in April '98 a cloudy time of year on the Red Planet."

The picture could just be some dust that has moved around a bunch of time at had made a face figure out of the dust and debre. The pictures also look different over time which was probably the dust and sand moving it all around. Plus there are really strong and heavy storms almost every single night at mars. so the dust, sand, and rocks are flying every where so that can cause disfiguer to anything. So before you jump to conclusion about it being aliens you should know more facts about what happens in mars on a day to day basis.