As title said. Lately there lot rotated image (without any modification (duplicate)) uploaded here. It's okay to upload rotated image even though the original image already exist (no matter what the original looks like)? What happen to rotated image already uploaded here, kept them or no?

I'm personally not fond of. Especially considering that some of them are subjective, rotating to an apparent "correct" orientation would just ruin author's artistic intent.

At the very least, the original should always be uploaded.

So that's mean uploading rotated image is not allowed?

Few original image/posts has been replaced with rotated image before. Moonian also give reminder to not upload rotated image, but user keep uploading them. If keep like this, people will spam the site with rotated image.

Looks like they keep it up.

if it's a scan, just rotate it or whatever.
if it's a digital source and clearly need rotation, rotate losslessly either through jpeg transformation if possible or otherwise exif tag (with exiftool or similar). Don't rotate jpeg and save it as png. If it's ambiguous just leave it as is.

So it's not count as duplicate?

Don't upload the unrotated one