Hello Fred,

Thank you for reaching out and I am happy to help!
This indicates that you have enabled the Lazyloadin option in the W3 Total Cache, and what you are referring to is a placeholder that is used in those cases.
This is perfectly normal behavior and it does not impact the website performance or act as an external resource.
As the user scrolls down the page, the image placeholders start coming into the viewport (visible part of the webpage). We trigger the load for these images when they become visible.
I hope this helps!
Thanks!