With some matrix manipulation, I've issolated the coin borders:
Isn't that something which Mathcads Image Processing Tools can do out of the box? There are quite a couple of different Edge detectors available to chose from. How to automatically chose appropriate parameters for pics with different intensity gradients may be the next question. I'm no expert in image processing but I could imagine that some of Mathcads analysis histogram functions could help in finding those values. Maybe it even makes sense applying levelmap() or equalize() before going to the edge detection so that there is a uniform transformation on intensity levels throughout. Just some thoughts, no expertise.
BTW, I guess that detecting and counting blobs could be easier if the shapes are fully filled.
One way I could image to count blobs could be to run through the pic (I assume filled blobs as at the bottom right) and when you arrive at a white pixel, you apply some kind of floodfill algorithm - without changing the pix, just to get the dimensions of the object (so you don't need a full fledged floodfill, just be sure to get width and height of the object). Collect the rectangles found that way in a list and go ahead scanning the pic. For every white pixel you check if the coordinates of the pixel are already inside one of the rectangles in the list, if not -> new rectangle found.
In case you didn't notice: In the bottom right pic I was cheating as I told Mathcads reg_grow() to color 10 regions, so i was using already the known number of coins ;-)
