Default Picture appears unwanted

My website works well, but there is one thing that bothers me: When i set a link in a facebook post, the Facebook system grabs a default picture from whom i didn’t know that it still exists on my server. I don’t know how to avoid that. How cann i delete this picture from the server? Thank you in advance.
Regards, Harry

Hello Harry, please check this link, it might help:

Please feel free to ask any other questions that you might have.

Kind Regards, Roman.
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