Here you go, all 3 image types:
https://twitch-tools.rootonline.de/show_all_channel_previews.php?filter=logo
https://twitch-tools.rootonline.de/show_all_channel_previews.php?filter=profile_banner
https://twitch-tools.rootonline.de/show_all_channel_previews.php?filter=video_banner
Be aware that just because you can doesn’t mean you should. Especially the video_banner (offline images) are pretty big so it’s not unlikely that your browser will hang or crash. Also the 3 links above will only show channel which have the corresponding image (and are currently
online), just FYI.