First, you should know that ShortPixel Image Optimizer does not apply any lazy-load effect to your pictures. Here you can read more info about it.
If you want to combine our plugin ShortPixel Image Optimizer with a lazy-load effect, you can use Autoptimize for this. Just install it, go to Settings > Autoptimize > Images, and enable the checkbox called “Lazy-load images?”:
That’s it!
Please note that enabling the first option “Optimize Images” will serve your images from ShortPixel’s CDN. Here’s more information about it.