Image in README.md gets truncated after some time

I like to include images and even animated gif’s in my README.md file. I do this by linking to an external server hosting the image/animation. Initially, everything works. After several weeks, suddenly these images/animations appear truncated when viewing the repo. For images, only the top part is shown, and for animations only the first frames are shown. As an example, see this repo of mine.

What can I do for this not to happen? I would like to keep the images/animations as external links, rather than including the files as part of the project. I could rename the file on the server and edit README.md accordingly, which will reset the image, but it will break again in a few weeks’ time. I know that GitHub uses Camo for all such images/animations, and I have even tried the curl -X PURGE trick from here, but to no avail.

I’m not seeing anything on that example repo’s README that looks broken. Is there something specific I should be looking for?

The image is back again! Maybe the curl trick worked anyway, but with quite a time delay.