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You can do the following:

1. find contours on this image, which is already binarized with black background so it's ready for contouring (https://docs.opencv.org/3.3.1/d4/d73/tutorial_py_contours_begin.html)

2. for each contour there are APIs to calculate perimeter, area and center of mass (moments) https://docs.opencv.org/3.3.1/dd/d49/tutorial_py_contour_features.html

3. Of course you will easily be able to count contours