When you drag your Image Safe Stack out, you will see the above stack appear on your page.
Now simply add the image you want to keep safe.
You can even use warehouse images.
When you select this option, the stack settings will change. You will need know the size of the image and have a URL to enter in the stacks settings.
If you want to protect all of the images on a page, you can do this as well. Check the box by Protect All Images?
Now read the warnings in that image.
Now preview and enjoy! For an overview of the remaining settings please refer to the Image Safe Settings section.