For permanent links you can use: https://ezgif.com/reverse?url=http://example.com/image.gif
Online GIF reverser
This tool allows you to easily and instantly reverse animated gifs.
It is also possible to make a GIF that runs in one direction and then reverses back to the start, for seamless looping.
Use GIF effects tool for more advanced options.
Upload an image by URL or select a file from your computer.
You can also use ezgif to reverse a video.