Here are some tips to help you :). Mind you, these are only useful if you are using a phone. I am unfamiliar with using Wattpad on a desktop or laptop. I don't believe links show up as images on those, but I could be wrong.
Make sure that you're clicking on "Open image in New Tab", then copying the link of the new tab that pops up.
It's possible that you may have to do it twice because sometimes the phone automatically downloads the image for some reason, instead of opening a tab :/. Or your phone may be blocking pop-ups in its browser settings.
If by chance you're clicking into the gif (and seeing this kind of page https://tenor.com/view/husky-pun-dog-meme-gif-9639526), instead of just tapping and holding down on an image from within the search results (from this kind of page https://tenor.com/search/dog-gifs), Here are some steps to help you. Tap on the image itself (on this page https://tenor.com/view/husky-pun-dog-meme-gif-9639526). A small box will show up that has two options to COPY URL or DOWNLOAD. Select COPY URL, and in your clipboard, there should now be a ".gif" link that should work in wattpad (for a gif or image to show up in a comment, it needs to have a ".gif" or a ".jpg" or a ".png" at the end of it). And be sure to delete any of the text or numbers after the ".gif" part of the link. For instance, of https://media1.tenor.com/images/c9fd3f5ad87f9c9ae12a8e70aa0d14a5/tenor.gif?itemid=9639526 , you only want https://media1.tenor.com/images/c9fd3f5ad87f9c9ae12a8e70aa0d14a5/tenor.gif