I've tried to compress the following GIF with RIOT 1.0.1:
https://upload.wikimedia.org/wikipedia/commons/2/2c/Rotating_earth_%28large%29.gif
However after I opened the image with RIOT, both initial image and optimized image lost animation frames, only the first one preserved and compressed. It's a sad thing for loyalty RIOT user that all animated GIFs becomes static after the optimization, I suggest the RIOT should be able to detect every frames of GIF, optimized them, and keep the file animatable.