Spotting aliens and bits of spacecraft on Mars has been a full-time occupation for believers in the nearly 40 years since humans first started getting decent images of the red planet.

It was this "face on Mars" picture from Viking 1 that first ignited the hobby.

It was also this picture that raised greater awareness of the psychological phenomenon pareidolia — essentially, the mind being stimulated to see things that do not exist.

Creationists in particular love to use pareidolia as an explanation of why paleontologists see "fossils" where they see "unusually shaped rocks." And when it comes to confusing rocks with evidence of alien life, it doesn't get much better than scrutinizing the images NASA posts daily from its Mars rovers Opportunity and Curiosity.

In fact, we've got a whole collection of them here, from a dinosaur spine to an ape lady working on her tan.

The latest instalment, however, is undeniably intriguing — even as a rock formation:

Here's the full-size pic from NASA.

Take a closer look.

Here's the ultra-zoom, which has been clarified a little by several alien-spotting websites.

It's got them all in a tizz, and many are calling for NASA to send a rover back there to clarify what it photographed. If it's still there …

Seth Shostak, senior astronomer and director of the Center for SETI Research, is not among the believers. He told The Huffington Post he got images like this one "about once a week."

Sometimes, pareidolia means seeing isn't believing.

But not always.