If you need to share a screenshot quickly online, you're going to need help from an app.
For single screenshots or video recordings, use Capto or Dropshare. Both make the process simple and both are fully integrated with major cloud sharing providers.
If it's a GIF that you want to upload, Gifox is the go-to app. Capture your GIF and use Gifox's drag-and-drop tool to upload your creation to Slack, GitHub, imgur, Google Drive, and more.