Smush

Smush (developed by the massive WordPress agency WPMU DEV) is arguably the most recognizable, heavily installed, and widely utilized image optimization plugin in the history of the WordPress ecosystem, boasting millions of active installations. It built its massive empire by offering an incredibly generous free version that solved the fundamental image bloat problem for everyday bloggers and small businesses. The absolute core superpower of Smush is its "Bulk Smushing and Native Lazy Loading." A user can install the free plugin, click a single button ("Bulk Smush"), and the software will systematically go through their entire media library, losslessly compressing thousands of images. Crucially, Smush also includes built-in 'Lazy Loading' (preventing images at the bottom of the page from loading until the user scrolls down to them), which drastically improves Google PageSpeed scores. While the free version is restricted to lossless compression (and a 5MB size limit), the Pro version unlocks aggressive lossy compression and a global CDN. For millions of entry-level webmasters, bloggers, and small agencies, Smush is the absolute default starting point for image optimization.