Great photos for a great topic @marcorp!
Are you aware of @TerryPG’s series on murals? Here is one example with links to the other episodes: Small Towns Local Murals, Part5 . My comment to Terry’s article explains just another facet of graffiti, I found 14 years ago in Rome.
I agree with
I would even say, there is a big gray zone between graffiti and murals. But poor graffiti can also destroy planned murals as this example shows: Google Maps
In my home town, Mönchengladbach, Germany you can apply for painting well defined walls. One example: Google Maps.
An example for planned, artistic murals is Mugnano, a small fraction of Perugia, Italy: Google Maps