Add own logos to operators

I'd like to be able to add logos to the operator fields when creating a new trip. It's only a minor thing but for instance, I've put the London Underground Lines as their own operators and there are no logos for them so I'd like to be able to add my own so some pictures show up when in the Trips feature. The same can be said for smaller companies as well that do not have their logos premade into this brilliant website, it'd be great to be able to add your own to fill the gaps in.