An image can be optimized inside WordPress and still be served as the original JPG or PNG on the frontend. This is the difference between creating optimized files and delivering those files to visitors.
Optimization and delivery are different steps
Media Library optimization creates smaller files, WebP variants or AVIF variants. Frontend delivery decides what the browser receives when someone opens a page. A theme, page builder, CSS background image, CDN or cache layer can still point to the old file even when optimized variants exist.
What a safe plugin should show
A good WordPress image optimizer should make this clear. It should keep backups, avoid replacing files blindly, and give site owners frontend delivery controls that can be tested before bulk changes are made on a production site.
Recommended workflow
Optimize one test image, open the page in Chrome DevTools, check Network → Img, and verify whether the delivered file is WebP/AVIF or still the original. Clear cache after changing delivery mode.
