title: grafana - alerting via slack, images aren't showing up
body: <p>I'm trying to get graphs to show up in my Grafana v4 alerts in Slack.</p>
  
  <p>When i use the test notification button, I get a pretty graph.</p>
  
  <p><a href="https://i.stack.imgur.com/rk8e1.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/rk8e1.png" alt="Alerting via Test Notification"></a></p>
  
  <p>However, when my alerts go through no graph :(</p>
  
  <p><a href="https://i.stack.imgur.com/Yk080.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Yk080.png" alt="enter image description here"></a></p>
  
  <p>Here are my logs when an alert is triggered:</p>
  
  <pre><code>t=2016-12-07T10:43:01+0000 lvl=info msg="New state change" logger=alerting.resultHandler alertId=1 newState=ok prev state=alerting
  t=2016-12-07T10:43:01+0000 lvl=info msg="Sending notifications for" logger=alerting.notifier ruleId=1 sent count=1
  t=2016-12-07T10:43:01+0000 lvl=info msg=Rendering logger=png-renderer path="dashboard-solo/db/sample-alerts?&amp;panelId=1"
  t=2016-12-07T10:43:07+0000 lvl=info msg=uploaded logger=alerting.notifier url=
  t=2016-12-07T10:43:07+0000 lvl=info msg="Sending notification" logger=alerting.notifier type=slack id=1 isDefault=true
  t=2016-12-07T10:43:07+0000 lvl=info msg="Executing slack notification" logger=alerting.notifier.slack ruleId=1 notification="Slack #skyline"
  
  t=2016-12-07T11:05:17+0000 lvl=info msg="Initializing Alerting" logger=alerting.engine
  t=2016-12-07T11:23:35+0000 lvl=info msg="New state change" logger=alerting.resultHandler alertId=2 newState=alerting prev state=pending
  t=2016-12-07T11:23:35+0000 lvl=info msg="Sending notifications for" logger=alerting.notifier ruleId=2 sent count=1
  t=2016-12-07T11:23:44+0000 lvl=info msg=uploaded logger=alerting.notifier url=
  t=2016-12-07T11:23:44+0000 lvl=info msg="Sending notification" logger=alerting.notifier type=slack id=1 isDefault=true
  t=2016-12-07T11:23:44+0000 lvl=info msg="Executing slack notification" logger=alerting.notifier.slack ruleId=2 notification="Slack #skyline"
  </code></pre>
  
  <p>I attempted to configure the s3 buckets which I may have done incorrectly, but i'm surprised to not see any error messages in the logs if that was the case.  Some of the log messages indicating a rendering action and others dont.</p>