What program to use for batch image processing?

Question

Windows

the program must be able to:
multithread,
have a filter for images (like adjusting the gamma or make the picture black and white),
not fail when adding 100k images.

Answer 1

In my opinion FastStone Image Viewer is the best option. Batch conversion is available. I can’t judge about 100k photos at a time, but I processed 300+ without problems

Answer 2

Why do you need multithreading? What operation on the picture do you hope to effectively parallelize? Are you sure this is possible? If you mean simultaneous processing of several pictures, then this is a little different. Just run several instances of the program, each with its own bunch of files, and then let the OS have a headache for parallelism.
Well, examples of programs have already been named.

Answer 3

I am using XnConvert. I won’t say for 100k images, I didn’t try it, but I fed several hundred.