Allow others to collaborate on markups with you. In the upper right hand corner of you markup toggle the markup privacy setting to "Collab".
Then share the markup link with any Hero or Superhhero user you want to add their own layer of annotations to your markup. Each markup allows for up to 20 collaborators. As the owner of the markup you can always remove any collaborators. By default only your annotations show to a viewer.
As a collaborator click the Collab or Start Collab buttons to create your own layer of annotations on a markup.
As a collaborator you can use all the tools except Blur, Crop, & Rotate. Only owners of a markup can use these tools.