I use a website auditor to analyse my new site build. It’s been flagging up that I should minify my images. I performed the tasks required but it still kept flagging up. I then clicked on the flagged image URLs in the auditorand was amazed to see that they were the original stock images used in the template. Therefore it appears that replacing images isn’t removing the old ones from the project.
I did read in a post about going through the old versions and deleting from the cache but I seem to have loads of versions and it seems to be a hammer/walnut scenario.