I'm thinking we could include the year (approximate) when the picture was taken in the "credit" field, and hide/replace those that are too old. Ie.- "Official Site (2010)".
Ex:
http://vgmdb.net/artist/331 comes from a ~15 y.o. official site.
From what Cedille said about composers complaining, I don't think they'd like ooold images, even if these were 'official' at some point (ie.- from old albums). People and fashion change, etcetera.
And in general, I agree only accepting official+sourced pics is for the best (respecting privacy is important).