Since WordPress 4.4 release of December 2015, native responsive images is supported by srcset and sizes attributes.
By adding srcset attributes for responsive images, it allows browsers to choose the most appropriate image size based on the user’s device.
WordPress automatically creates several sizes of each image uploaded to the media library. WordPress Core includes a default set of image sizes (i.e. full, large, medium_large, medium, thumbnail) and those sizes are included in the srcset value for an image.
Themes and plugins can register custom image sizes, which will also be added to the srcset.
Before responsive design was popular, many sites attempted to dynamically serve different layouts (including images) to browsers based on the device type (e.g. phone, tablet, etc.). In these cases, all of the dynamic stuff happened at the server, before the page was rendered. This strategy is usually associated with the term adaptive design.
Responsive design, on the other hand, uses tools like media queries to allow a single page to be rendered that will respond in the browser based on things like viewport width and display density.
Responsive images follow the second strategy and sends all of the information to the browser up front and lets the browser take care of loading the appropriate image rather than making those decisions on the server before the page is loaded.
Image instead of being served an overly large image and resizing down to fit the space
Responsive image is just stupid bad. It solves an aged problem of internet connection speed and image compression. Responsive image does nothing but generate unnecessary, redundant and low quality data.
It’s too late for me on this project. But never again.
Most of us care about our storage space. We pay for it, it makes our backups huge, and it’s LITTER.
No, I don’t want WordPress generating 4 sizes of each image I upload, compounded by the 3 or 4 extra sizes that the theme requests. Most users are literally hosting about 10 variations of every image they upload.
It’s truly insanity.
WordPress is over-reaching again. This time it’s some excuse about responsive image sizes.
I’m more than annoyed. Watch your backs. WordPress is sneaking in all kinds of crap, not telling us about it, and removing the ability to turn it off (like the REST API, which left millions of sites vulnerable to hacking, and they WERE hacked too.)
This is one way to temporarily-permanently (because WP will screw us again somehow).