Segmentations outputted by this web tool are integer-signed images.
A value of 0 corresponds to background, and each subsequent integer corresponds to a unique cell (e.g. pixels that are 1 belong to the 1st cell, 2 to the second cell, etc.)
We've provided a few scripts here to show how you can upload this convention into Python, R, or Matlab for subsequent analysis.
Python
Matlab
R Script
ImageJ Instructions