You can find animated Gifs all over the internet. A great website for finding a large collection of them is giphy.com. Once you find them, you'll need to get them over to your Raspberry Pi. The easiest way would be to just use FTP or downloading them directly from the internet on your Pi if that's what you would prefer. Just make sure they're in the same folder as the script.
To use the player, open up the command prompt and go to the folder where the script resides. Make sure you have placed all of your animated Gifs in this folder. Once that is done, go ahead and run the command:
You should see the animation running on the display:
Some animated Gif files have a limited number of loops, some will loop indefinitely, and some will just play once. If you have any that don't play indefinitely, then the player will automatically advance to the next animated Gif.
If you are viewing one that loops indefinitely, you can get it to advance by pushing the button for advancing to the next image or pushing the button for going back to the previous image.
There's definite improvements that can be made to this player, and we wanted to publish what we had to get folks started - feel free to contribute and have fun!