Oh, okay 
Sounds cool with a plugin. Would like to test that.
It’s barely a script, actually. It’s a command that takes images a.png and b.png from the desktop. It takes the height of the larger of the two and resizes the smaller one until it has the same height while keeping aspect ratio. It then combines the two, where it places a.png next to b.png. A on the left and B on the right.
The resizing part isn’t really necessary, actually. It could just as well fill it with transparent if PNG or white if JPG.
This iOS workflow/shortcut does something similar:
https://www.icloud.com/shortcuts/9a1c4dee622e4de5a5a63960c0714c1b