Right click on the image, and it should give you the option "copy image source" or something like that, or it might give you view image. That should take you to a page with just the gif on it. C&p it's web page URL thingy, as that's the page source.

Then when you try to add a pic on a post, it has a load with URL option or something, so just paste it there. Also I find you have to make sure 'original image size' is selected. If you want to change the size you can do it after, but if you try to change it when embedding it, it won't work.

Hopefully that makes sense : ) xx