Greta works by hooking in as early as possible onto the loading of your images, so we can process them through our pipes. This works best if you put the script high up in your header, as it will allow the script to pick up as many content as possible.
We load images as they enter the scope of view of the user (lazy-loading). This feature allows you to save a substantial amount of bandwidth, while enhancing the user experience because the content that the user actually sees will be loaded in priority - the best of both worlds!
You can also decide to manually set what content to load or not load using Greta - more information on this here. We also support using Greta for background images. If you want to migrate your existing lazy-loading library to Greta, the instructions are over here.