I was going to waffle nostalgically about old software and the the good old days being better than today, but out of curiosity I was searching for commandline tools or scripts to do the job, and found this on Ask Ubuntu, ironically, since it's a Windows program:
https://www.andreaplanet.com/andreamosaic/
I'm not sure if the free version is enough for what you need, and it seems to have small watermark in the corner, but maybe that's no problem.