Hi,
we have the same problem described here, not in User Profile but in Administration>Setings>Navigation menu.
While in Profile you can access not as an administrator and have the upload tab, this is not possible in Administration>Settings that you can use only as an administrator.
It is possible to avoid the problem uploading the desired image somewhere else and pasting the URL but we think this is a bug that should be solved; in OJS 3.1 was possible to upload images also as administrator.
Best regards
Stefano