Best algorithm or other solution for photo compare

Have a bunch of pictures I want to compare to track down the duplicates except the backup. It's kind of "mess" right now with the structure.

Was thinking of making a powershell script and wonder if "Get-FileHash, such as SHA256, SHA512, or even SHA1" should work OK for this? Or is it any better method?

Get-FileHash should work just fine. I would recommend using SHA256, while slower it has a nearly 0% chance of having a collision (meaning where two non-duplicate files end up having the same hash).

I use VisiPics for that task, it works pretty well. You can tune it to select how close a match you want, and it takes the resolution of each picture into consideration. It worked great for sorting out my downloaded wallpaper files, I just grabbed a bunch and then sorted out the duplicates. :)