Some InChI’s are short, such as that for methane: InChI=1/CH4/h1H4. Others are long (think crambin ), and you don’t want to show them inline. Or you just want to show them anyway, but still want the chemistry to be understood. Here come the invisible InChI’s. Alt text for images One solution is to put the InChI as content of the @alt attribute of the HTML <img> element.