How the f do you post an image in here?!?!
I download the image, then in "More Reply Options" on the desktop site, you can attach (upload) it, then "Add to Post". Seems to be the most reliable method for me.
Or ... if you have a link from the internet of the image or gif you want to use and are using the full editor on your desktop, click on the 'image of a tree' icon and follow the prompts.
Or, as spycake noted above, click on 'More reply options' and follow those directions. Those instructions work for downloaded images and photos.