I thought this was a feature for a while because image hosting sites like Imgur convert animated GIFs into videos because the compression is better, and you can adjust the playback. Some of them will even keep '.gif' in the URL despite serving you a video instead.
This is particularly infuriating when you're trying to use google image search to find a gif to embed in an html frame that doesn't accept videos and all you get are gifs that turn out to be videos.
