i think imgur compresses the img files upon upload or something, cuz there’s noticeable degradation in image quality for some of these wallpapers - especially if it has a really smooth and subtle gradient.

tineye is good for searching up other instances of the same image though, at least for some of these more popular images. here’s the biggest resolution available from tineye. And here’s a link to the artist’s tumblr with the original files (that i also found through tineye)