Why does Google Page Insights still recommend optimizing images? (BIE)

It's possible that Google PageInsights might report that your images need to be optimized even after you have compressed them in our Bulk Image Edit app.

There are several reasons this might happen. Here are the most common:

1. Only targeting the homepage: When you test with Google PageInsights, it is usually the home page being tested. To test the effect on product page, please make sure a URL of a particular product page is submitted for testing. We recommend testing a product page before optimizing, and then again after the optimization.
2. The image resolution is too high: If your product pages are still loading slowly, you may need to reduce the image resolution. For example, if the images are 2000x2000 pixels you can resize them to 1000x1000 pixels. The new file size should be about 75% smaller than the original file.
3. Your theme generates large thumbnails: Google's PageInsights looks at thumbnails to determine whether they are larger than necessary. This has nothing to do with compression - it is determined by your theme when it automatically generates thumbnails. Therefore even if you shrink the images and reduce your loading speed, it will still detect a large resolution and dock you points. All responsive themes suffer this to some extent, although some themes are better at it than others.