I was also having the same problem, with about 15 images (logo twice and others were in a widget sidebar). Each time the website was opened about 5 Mb traffic was generated (with PHP as user agent) and loading took lots of time.
I deactivated all plugins, and still saw my site generating the above mentioned call but only with logo image. So I concluded it must be the probmme with the theme.
This led me to “getimagesize” call in the “parts/class-header-header_main.php”, which when commented would omit having the logo being fetched from inside of the server.
Also it turned out widget in sidebar used same method, commenting it there as well, speed up my site about 400% and no unecessary traffic is generated any more.
Hope it helps.
