I like the amazing FastStone Photo Resizer but I would not complain if it was a little faster. It is a Quad Core for God’s sake!
Thanks to Renan Duarte I found a C# code for a batch photo resize. The only thing I have to do is insert a loop (it is named “C# Batch Photo Resize” but a button has to be pressed for each photo processing) and include multi-thread capability.
FastStone has more complex algorithms and it is already done, but this will be small step before learning the algorithms behind the scenes.