Image segmentation in open-source software

For Python, there are very few option for free source RS based image segmentation. I'll suggest two,

• Orfeo Toolbox: Probably the best free alternative of eCognition. It has quite a few segmentation module. Its available inside Python, in QGIS; even has its own gui alternative called Monteverdi.
• RSGISLib: Another Python library which also has a decent set of segmentation module. RSGISLib binaries are currently available for Linux and osx users only.

If it's not remote sensing I'll suggest OpenCV.

For segmentation, while you can probably go into the detailed statistical properties of the data (particularly for SAR), it is often a good start to assume that these are normal images/stacks of images, so standard image processing segmentation approaches will often work well. All you need to do is to read in the data as numpy arrays using e.g. GDAL/rasterio.

Once you have the data available, scikit-image is an actively developed image processing library with lots of useful segmentation algorithms and tools to help you understand the results.