I'm fine with this but I think it is up to you to re-evaluate:
 - Does it have to be a built image? 
 - Is there any chance of someone sharing / uploading a not-built but to-be-used-as-a-base image?

In these cases, should we say perhaps "share any image". Or even "submit"? 

The words "share" and "private" do not go hand in hand, really.