[free]

This is fine if you have a limited set of images that you handpick and optimize.

Do you have any suggestions when there are thousands of images and all this needs to be automated?

[icebraining]

Use GNU parallel: https://www.gnu.org/software/parallel/

It can distribute the work across the available CPU cores, and it can even distribute the work across different machines using SSH: https://www.gnu.org/software/parallel/man.html#example__dist...

[natch]

He has an example at his github link where he uses a simple bash for loop to do many images at once.

[medde]

but it does seem inefficient if you often have lots of images to process

[natch]

how so?