Unless you set a profile picture for a team, the team profile picture will match the organization's profile picture.
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In the top right corner of GitHub Enterprise Server, click your profile photo, then click Your organizations.  
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Click the name of your organization.  
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Under your organization name, click Teams.  
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On the Teams tab, click the name of the team.  
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At the top of the team page, click Settings.  
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Click Upload new picture and select your desired profile picture.  
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Click and drag to crop the image as needed, then click Set new team avatar. 