I've been having this problem since I have opera I believe, but somehow some twitch images like the ones in the "browsing" tab just doesn't show as they should.
This is how they look in other browsers.
And this is how they look in my opera browser.
I had this same problem with Twitch emotes and 7TV/BTTV animated emotes but i could fix it by changing dark mode in opera://flags, however i couldn't find any other solution to the first problem.