Random photo as dashboard

I am trying to create a playlist that would include one dashboard showing a random photo.

I have made a script that writes a new photo every now and then to /usr/share/grafana/public/img/photo.jpg.

Then I have a Text Panel with img src=/public/img/photo.jpg

The problem is that the photo doesn’t seem to update at all, even I have replaced the file with a new one.

Any ideas why this is happening? Is there a cache somewhere?