Particle tracking from image sequence

[Blodgett Mary]

Dear All,
I have a big problem in tracking the particles from these images.
I applied different masks and filters to have these 3 images, to me seems enough fine to let the software understand what is particle and what background but it is not.
My idea is to track the particles automatically and the final goal is to have a velocity profile (I know the conversion pixel/mm and the time shift between the images).
Please find attached the 3 images to understand which is my problem.
I hope to have some feedback to understand which is the main limitation in my workflow.

Plugin used: Tracking-> TrackMate


Thank you so much,
Cheers
Mary