I am trying to display the owner chatter picture in a lightning component and I am unsure if this is a second query that should be done in the controller or a helper as I have seen some threads using a function to query it and some using apex however none are asking about this for a lightning component, this was pretty simple on a custom lookup field just the standard owner field has it's limitations and the field is not available in a formula field.

Apex controller: 

public class Case_List_DPI_Controller {
  @AuraEnabled
  public static List<Case> getCases() {
    return [SELECT Id, Subject, CaseNumber, OwnerId, Owner.FirstName, Owner.LastName, Owner.Name, Owner.Email, Case_Life_Days_Business_Days__c, Case_Life_Hours__c, Case_Department__c,
            RecordTypeId, RecordType.Name, SourceId, Reason, Origin, ClosedDate, CreatedDate, Description, isClosed
    FROM Case 
            where Case_Department__c = 'Property' AND isClosed = false ORDER BY createdDate DESC
           ];  
  }
}

Component: 

<aura:component controller="Case_List_DPI_Controller" implements="flexipage:availableForAllPageTypes" access="global">
  <aura:attribute name="cases" type="List" />
  <aura:handler name="init" value="{!this}" action="{!c.doInit}" />
  <!--
    Use a data table from the Lightning Design System:
    https://www.lightningdesignsystem.com/components/data-tables/
  -->
  <table class="slds-table slds-table--bordered slds-table--striped slds-table--cell-buffer slds-table--fixed-layout">
    <thead>
        <tr class="slds-text-title_caps">
            <th>
                <div title="Open Cases with Property Department">Open Cases with Property Department</div>
            </th>
      </tr>
      <tr class="slds-text-heading--label">
        <th scope="col"><div class="slds-truncate" title="B. Days">B. Days Open</div></th>
        <th scope="col"><div class="slds-truncate" title="Owner">Owner</div></th>
        <th scope="col"><div class="slds-truncate" title="Type">Type</div></th>
        <th scope="col"><div class="slds-truncate" title="Subject">Subject</div></th>
      </tr>
    </thead>
    <tbody>
      <!-- Use the Apex model and controller to fetch server side data -->
      <aura:iteration items="{!v.cases}" var="case" indexVar="index">
        <tr>
          <td><div class="slds-truncate" title="{!case.Case_Life_Days_Business_Days__c}">{!case.Case_Life_Days_Business_Days__c}</div></td>
          <td>
              <div class="slds-truncate">
                  <span class="data-social-photo-guid-4eded8ac-41d6-4524-ab50-b14d0349f58d photoContainer forceSocialPhoto_v2 forceOutputLookup">
                      <span class="uiImage">
                          <img class="smallSocialPhoto circular" src="{!c.Owner.smallPhotoURL}" />
                      </span>
                  </span>
                  <a onclick="{!c.navigateToUser}" style="width:100%;" data-index="{!index}">{!case.Owner.Name}</a>
              </div>
          </td>
          <td><div class="slds-truncate" title="{!case.RecordType.Name}">{!case.RecordType.Name}</div></td>
          <td><div class="slds-truncate"><a onclick="{!c.navigateToRecord}" style="width:100%;" data-index="{!index}">{!case.Subject}</a></div></td>
        </tr>
      </aura:iteration>
    </tbody>
  </table>
</aura:component>