Today, I found out Codeforces' Hidden Feature. Look at the following. My large profile image and small profile image are different!
I can't believe this!
Look here and here. Still not convinced? Upload this and check how your profile images are changed.
Why this works?
I uploaded this to change my profile image. The result was amazing. Large profile image is almost black, but small profile image is white. It seems that Codeforces' image scaling algorithm is Nearest-neighbor interpolation. Nearest-neighbor interpolation uses data of a few pixels. If we therefore, 이 픽셀들에 두 개의 이미지를 나눠서 저장한 뒤 업로드하면 두 이미지를 다르게 설정할 수 있다.