After this post on hackaday.com my page got a lot of hits. I was using dropbox for hosting the images which maybe wasn't a good idea. They have a 20Gbyte limit per day for accesses to public links. Although I find it very unlikely that this limit has been exceeded, Dropbox claim so. To solve this problem for now I upgraded to a pro account at 9.99 euro per month. But this is not a permanent solution. I need to find a better and cheaper image hosting service. I have been looking at picblaze. Maybe it is the solution.