What is an Image Group?

In Image Optimization we refer not to “images” but to “image groups.” So, what do we mean by that?

When you upload an image to your Media Library, a collection of differently-sized versions of that image is created. These versions make up an image group.

Here's an example:

You upload an image called 770.jpg.

WordPress creates a collection of new images from that one:

770-1024x701.jpg
770-150x150.jpg
770-300x205.jpg
770-348x445.jpg
770-568x725.jpg
770-768x525.jpg
770-78x99.jpg

These new images, plus the original, make an “image group.” (The sizes in this example may vary from those created by your own WordPress installation, depending on your media configuration.)

When you run Image Optimization, all of the images within the image group are processed together, adding WebP and .bk images to the group, wherever appropriate.