Um, yes. The picture should be either actual allowed photography if the utaite, a representation of the utaite sponsored by them (i.e. in an avatar, album art, or a song video) or some symbol associated with them, such as a logo. Thus, fanart is not allowed. I think.
If we're talking about the main picture for an utaite and no pictures with the above criteria are high quality/appropriate/representative, such as on himawari's page, then the second best option is to use an avatar of the utaite used in a chorus or something, hopefully by an artist that the utaite has worked with before.
Finally, whomever's art you post, it should come from an artist who does not explicitly forbid reprinting. I'll check the site of any uploaded artwork if the site's in Japanese.