This is from Opportunity, Sol 028.  The original image is here at the NASA website.

   This is one of the most interesting organisms in that it shows many fine features, but they are hard to make out for the uninitiated.

   Unless you are familiar with microfossils, or marine fossils, there are telltales that you are very likely to miss.  The cleft on the left side is very clear, but what it says may not be.  Other things are the faint lines that seem to outline plates or armor.

   Let's see what we can extract and enhance using simple anti-shadow and differential techniques.

   The first step is to duplicate the image and invert it like a negative.  Then it is blurred heavily to produce a blobby sort of shape that has no details at all.  This is our anti-shadow.

   By subtracting the lighting from the image, what will be left is the detail data only- the raw shapes and forms without the range of brightness that can hide details from the human visual system.

   Now we add this to the original image and generate a new picture that has nothing but the difference data.

   I have enhanced the contrast by about 60% to sharpen up the features and make the image more easily seen.

   Right away you can make out details about the cleft and the outlines.  The surface shows many tiny bumps, typical for sea urchins.

   Many people have never seen a dead sea urchin- the shell is a thin structure of calcium carbonate, thicker and more durable than an eggshell, but not by much.

   It is covered with tiny bumps and pores.  The bumps are where the spines were attached to it when it was alive.

   Here is the resulting frame.  See how the features are much sharper now?  The outlines and bumps are clear and sharp and the ratio of bright to dark is more favorable.  We can see things that were either washed out or hidden in shadows now.

   Now, I have also taken the differential data and marked it to show the features as they are.  I have only marked a few, as it will get cluttered very rapidly.

   We see little more than noise in many images, unless we are already familiar with what we should see.  This work provides the path that shows you what you were missing.

   And on examining the original image, you can clearly see that these features were present all along...

   There are so many similar features on so many of the fossils that it would be silly to refute them.  This is definitely a fossil organism, and no mineral process can produce this sort of marking at so fine a resolution.  These markings or similar ones are on nearly every spherule- determined only by their species.