I think you've borrowed the thumbnail picture from a post of @mercurial9.
If I'm not wrong... that thumbnail is something that @mercurial9 made himself/herself and in that case, you should ask for the permission of the original content creator and I hope you got that and still, you should credit the original creator also in your post in order to use something that not yours.
Otherwise... you might get in trouble in the long run as this is what we know as plagiarism.
Please let me know if I'm wrong.
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