In a an image with sufficient contrast between the foreground and the background, thresholding and using the fast radial symmetry transform[1] should do the trick. I have some really old code that I wrote a few years back that does something similar. I was able to use the same algorithm for counting objects in images captured from a Neubauer chamber [2] and saved countless man hours at my university.

Disclaimer: the project is really old, and from a time when I barely knew how to code. Lots of bad coding practices et al.

Github: https://github.com/vibhuagrawal14/segmentation-of-overlappin...

[1] https://link.springer.com/content/pdf/10.1007%2F3-540-47969-...

[2] https://www.researchgate.net/figure/Images-of-Canis-familiar...