From their Terms and Conditions I found this.
Stuff not to do
If someone else might own the copyright to it, don’t upload it. Don’t upload gore, obscenity, advertising, solicitations, "hate speech" (i.e. demeaning race, gender, age, religious or sexual orientation, etc.), or material that is threatening, harassing, defamatory, or that encourages illegality. Don’t hotlink to such content, or to file-sharing or torrent sites. Don’t be a troll or a jerk. Don't impersonate someone else. If you do (and we will be the judge), or if you do anything illegal, in addition to any other legal rights we may have, we will ban you along with the site you're hotlinking from, delete all your images, report you to the authorities if necessary, and prevent you from viewing any images hosted on Imgur.com. We mean it.
Meaning that you cannot hotlink the images but can only share the image path. Plus even if you managed to hotlink it and bbcode into our site, we would get into trouble.