Recently, while trying my luck with adding a little GIF inside my WordPress post & soon realizing that it’s not at all working out for me. The image wasn’t animating.
Soon after I realized that something might not be right with uploading of the image. I re-tested the GIF on my machine & tried re-uploading it a couple of times. But that doesn’t work either.
After several attempts and disappointments, I found out the solution and it was damn pretty simple.
When you upload the new image, WordPress resized it for you whether you want it or not or until you tell your WordPress not to.
Same case is with the GIFs. The problem was occurring due to the cropped version of image I tried uploading. Cropping the GIF might cause it to break some frames and hence results in a regular image.
After uploading your GIF, make sure to edit the GIF and set the image to the full size. Which ensures that WordPress uses the original image you uploaded.