Uploading Image via Safari and Evernote

I am using a Mac OS X El Capitan. And I use Evernote Skitch to capture screenshot. When I copy the screenshot in memory and paste it into Discourse, it didn’t work in Safari (nothing happened). The same screenshot but paste into Discourse using Firefox is ok (it uploads).

See https://meta.discourse.org/t/paste-images-in-composer-not-working-in-safari/24632