I uploaded this piece to Newgrounds: http://www.newgrounds.com/art/view/blueneonkid/kirby-japanese-csp-brush-test
and during the upload process, the thumbnail cropper pop-up freaked out and minimized before I had a chance to crop the thumbnail.
I uploaded it anyway, but to my dismay, my picture's thumbnail is this.
http://art.ngfiles.com/thumbnails/542000/542051.png
QUE?! NANI?!?!?!! What is this?! Huh? What is this 3-color disgrace doing as my thumbnail? That ain't no son of mine! This doesn't do the picture any proper justice!
Well then, I decided to change it into this:
http://art.ngfiles.com/thumbnails/542000/542051.png?1503443135
But still, the thumbnail remains THIS abomination: http://art.ngfiles.com/thumbnails/542000/542051.png
How do I get my art thumbnail to change into the majestical preview picture it's meant to be?