program that stitches together a bunch of image files into one giant poster?

[madscijr]

imagemagick convert.
https://imagemagick.org/script/convert.php
...
(or +append) if you want horizontal

Interesting, thanks! I already use imagemagick to convert images from the weird new formats like webp not supported by certain apps, to formats they do understand, but haven't gotten too deep into the other features. This makes me curious to find out more about what else it can do. Thanks again!