Error loading image - camera, camera_proxy

I always get an “Error loading image” in frontend when I use the configuration:

- platform: generic
  still_image_url: http://[url of webcam]/cam.jpg
  name: webcam 

If I use curl with the appropriate url I get a image from the webcam. In the past this configuration was working perfectly.

Do someone experience this issue too? Could there be an issue with camera_proxy?