There's a couple of ways, please feel free to comment on this if I didn't help you.
1. Copy and paste the image
2. Upload an image by pressing the Image icon above the chat (I highlighted it below) I go to upload, browse, and send to the server and it will appear in your post. This is the preferred method so your image won't disappear down the line as its uploaded to TibiaQA's server.
3. If it's a Tibia Wiki image it's a known issue where they have an old URL that doesn't work. This is related to a previous question, Why am I having trouble seeing images? You need to change the image URL from static to vignette. To do this you can click on the image icon after clicking on the image, double click on the image, or right click and go to image properties. For example:
4. If you mean like make or create a gif image (like an animated image) you can use a site from google like https://giphy.com/explore/images and press create :)