I just published PerceptHash - a cross-platform #powershell module for image comparison using the dHash perceptual hash algorithm.
https://www.joshooaj.com/PerceptHash/
A few months ago I made a blog post about the algorithm and shared a PSM1 file with an implementation using the System.Drawing namespaces, but I wanted a cross-platform version so I rewrote it using the ImageSharp libraries in C# targeting .NET Standard 2.0, so it works great on Windows, macOS, and Linux.