program to run another program

No, in general. GUI programs are meant to be "user" friendly, where "user" != "programmer". Most GUIs are not designed with scriptability in mind.

Yes, it is possible to write a program to similate mouse clicks and mouse movements. The challenge is determining where and when and how to click. You use your brain and the clever vision system to do that when operating manually. Programmatically, you can't do that reliably.

Now, you know why I like CLI more? Ease of scriptability!

Few GUI programs (such as GIMP, Emacs) are designed with scriptability in mind. Sigh...

The problem is not the problem itself, but the tool you're using. It's not designed with scriptability in mind.

Why not use a scriptable program that can do what you want? GIMP can be scripted to do that, provided that you're willing to learn its Scheme dialect (Scheme is a dialect of LISP).

But why GUI when you're doing batch conversions? What's the point of displaying those images WYSIWYGly when all you want is just to save them back to disk immediately? Who is there to see the display?

So, ImageMagick is the tool that suits your needs. install it and then "man convert" to find out how to use it. You can then write a simple shell-script, or even 1-liner.

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