How to search by source?

How do I search images by source? like all images that are source from twitter?

source:*twitter.com* (though some are direct links, so source:*twimg.com* for those.) For pixiv you can use pixiv:any instead.

Talulah said:

source:*twitter.com* (though some are direct links, so source:*twimg.com* for those.) For pixiv you can use pixiv:any instead.

is it possible to search for source that is empty?

Yes, use source:none. It might time out so you'll have to filter by id or date.