Are the particles firmly enough edged that we can study distributions of shapes and sizes to find 'expected' size and shape and use that to assume boundaries between touching particles in order to count them individually? Or are the particles soft boundary (e.g., droplets of liquid) so each blob should be counted as one? We do not know.Are the wavelengths involved optical? Is, for example, this an x-ray image? We do not know.Are the particles generating their own light, or are they being distantly illuminated (e.g., starlight on a dust field in space), or are they being illuminated by room lights, or are they being illuminated by an instrument light specifically for that purpose? We do not know - and we do not know the spectral properties of the potentially illumination either, and those make a difference if we are contenting with any significant refraction.

Is the potential fluid diffusing the light in any significant manner? We do not know - just as we do not know the index of refraction of the potential fluid.

Is there a fluid involved? We do not know, and we do not know how thick it might be, and we do not know if the image is being taken from inside the fluid or from outside with a refraction boundary to take into account.Are the particles 2D or 3D? We do not know.Starting from the information that we have been given (nothing more than 'image' and 'particles'), you have multiplied hypotheses unnecessarily.

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