This and the pixiv source both are of about same size so "twitter copy" alone is not actually enough reason for deletion.

"twitter copy" was never a good reason anyway. The deleter should really specify whether it's higher res, less artifacts, or whatever the actual reason the other one is better to begin with instead of just blanket "twitter copy".

In the past twitter used to compress the image more heavily than pixiv. I'm not very sure how it is right now.

With that said, biasing toward one source over another is discouraged.

edogawaconan said:
This and the pixiv source both are of about same size so "twitter copy" alone is not actually enough reason for deletion..

Not only that. They even have the same quality.

Checkmate said:
In the past twitter used to compress the image more heavily than pixiv. I'm not very sure how it is right now.

With that said, biasing toward one source over another is discouraged.

It's way better now. I think even before the change there are some cases where twitter upload has higher resolution than pixiv.

This link explains the new Twitter specs.

https://twitter.com/NolanOBrien/status/1204557498990002176

I know no one has the time to check every single image, but if the dimension is identical and the filesize is similar, it is safe to assume they're the same image pixel-wise (and therefore no need to upload again).