You are getting this Error because you or your hosting company wants to load lazy images and you are using any lazy loader plugin on your website. Like Smush WordPress plugin or it could be any plugin. In my case, I was using the Siteground optimizer plugin that was encoding these images into data:images/gif code. When I was inspecting the website and it looks too boring URL. But after a to of research I came across this solution.
Deactivate the Siteground optimizer plugin and take a look at your website. It could be any cache plugin or image optimizer plugin like smush, wp-rocket, W3-cache something like that.