You can also simply drag and drop your image from your desktop into the text box of your Compose column.
You can select the "Hide Media" button, which looks like an eye symbol and appears once you have added an image. This will hide the image in your post by default, making it clickable to show the preview.
You can also attach video files or GIF animations to toots. However, there is an 8MB file size limit for these files and videos must be in .webm or .mp4 format.