I'm afraid it is currently not possible to upload an avatar for rooms, only for users and the group account itself. This is known requested feature, but I can't confirm if it will be available soon. Although feel free to vote and comment for it at:
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Background While our Hipchat server environment was reliable and performing well, as a significant and growing part of our business, the need to leverage the benefits of Hipchat Data Center&nbs...
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