The Graph Analysis Toolbox for MATLAB was written as a by-product of my PhD thesis. There is also a demo package available here. The goal was to allow for flexible representation and analysis of data associated with a graph, specifically slanted toward computer vision applications.
I wrote a short MATLAB function that runs the random walker image segmentation algorithm as an add-on to the above Graph Analysis Toolbox. The files contain a function to run the random walker algorithm and a script demonstrating its usage. The code may be found here.
Code to run the power watershed algorithm, including example usage, is available here.