To do it from imgur, press and hold the photo, select "share direct link" copy/paste the direct link into the post.
You can tell its a direct link because it will end in ".jpg" or whatever file type.
You can also upload directly from your instagram by using the menu in the top right of your insta post and selecting "copy share link" and pasting it into your post. Just mind the fact that anyone who clicks on it will be directed to your instagram page.
XXXclusive VIP members will be able to upload directly to the site by selecting "click to choose files" in the bottom area of the text box while you are creating a post.
From imgur or whatever host, right-click image and select "copy image address", paste it into the text box and it will auto-embed.
XXXclusive VIP can click "choose files" to upload directly.