Problem with http://i.ytimg.com/

Hello,

I deleted a video from YouTube, but an "image" remains online on Google Images. How can I remove it? It links to a URL like http://i.ytimg.com/
The webmaster tells me everything has been deleted.
On the Google Images side, the photo is still online, and I cannot request its removal as long as it is online.
Therefore, I need to delete it, but where is it? How can I access the server http://i.ytimg.com/?
Thank you,
Marie

Configuration: Mac OS X / Safari 536.11