Detecting multiple markers based on bright spots detection on raspberry pi 3

[Ofnuts]

I don't think you can go that route... attribute an id based on what? (hint: this criteria would need to be valid in both images). What you can do is measure the distance between the markers of the first image and those of the second, and see if some markers have remained within some distance of their original position, or in a more general case consider that the combo of markers in the 2nd image that minimizes the sum of the distances with the markers on the first image image is the new sequence of markers. In your example you would likely discover that M1, M2, M3 are now M2, M1, M3.