Blizzard is going to reward all viewers of Regional Finals and Summer Championship with two different portraits. To acquire one, you need to link your Battle.net account with a Twitch account. This should help you out to do so (just scroll down to the "HOW TO LINK YOUR ACCOUNTS" section). The nearest Regional Final you would like to watch to grab a portrait will commence this weekend. Tune in here to watch Europe Regional Final and get the portrait.
There are a lot of upcoming Heroes of the Storm E-Sport events, Regional Finals and Summer Championship, that can
grant you the award(s). Check this link to be more familiar with their schedule. Keep in mind that the reward, portrait(s), should appear in your collection approximately two weeks after the event’s conclusion.