There is one issue: some cities use the same logo (image file) as other, for example Hamburg and Berlin (yeah, most of this cases happen *at* Germany).

I can thing of two options:
1. we send the whole logo (`img` object) and create the ID by `img.src`+ `img.name` (without spaces)
2. make sure we have 1 image for each system, although, this will increase data traffic.