User blog comment:Harbumz/Introducing Vignette, Wikia's New Thumbnailer/@comment-3495717-20150212131246/@comment-24880673-20150213053533

Yes sometimes when thumbnailing an animated GIF you get artifacts. There are a few things that can contribute to this. One is the quality of the animated gif. Another is whether or not the image is being scaled up (output as a larger image than the original) when it's thumbnailed. A third is the thumbnail mode. For best results, I would suggest sticking to the scale-to-width and thumbnail-down modes for animated GIFs.

And yes, the animated GIFs remain animated with vignette. We are not freezing them or arbitrarily thumbnailing a frame.